Jim Rogers

Lives in Baton Rouge, LA, with two dogs, one cat, and one lovely wife. I'm a lead developer for GCR Incorporated.

Katrin and Jim

Month List

Forerunner 305 Battery Replacement

by Jim Aug 15, 2009 1:31 PM

My Garmin popped open on a ride recently. They want $79 to repair it, and I didn’t want to be without it for a while, so I did some research on fixing it myself.

A Look at the Case

Since the Garmin popped open of its own accord (probably because of the swelling battery,) I can’t give any advice on opening one - but you can find some here. There are no screws or clips; the two halves are just attached with some kind of adhesive.

Here is the bottom half of the case. Battery wires are soldered to the little circuit board, which presumably has the charging circuit in it. This board is also attached to the pins which go through the back of the case to the changing cradle, and it doesn’t appear that it can be removed.

IMG00031-20090810-1839  IMG00032-20090810-1840

The Battery

My battery was attached with a spot of some liquid adhesive; others may be attached with double-sided tape. I pried it out with a flat blade screwdriver with little effort, then clipped the wires near the battery, leaving as much as possible in the case.

IMG00052-20090810-1922 I don’t think the battery is supposed to look like this :-) It was clearly on the way to exploding, and needed to be replaced.

Finding a battery to replace the original one is the hardest part of this whole process. After much fruitless searching on the internet for an exact match, I gave up on finding anything. These Lithium Ion batteries require special charging circuitry, which is typically packaged with the battery cell. It’s hard to find a battery cell without the circuitry, never mind in this exact size.

In desperation, I decided to take apart the battery in my old Samsung Hue phone, which was sitting around, having been replaced by a Blackberry. Any Lithium Ion battery should work, from an electrical standpoint. They’re all 3.7 volts, because of the chemicals used, and the mAh capacity shouldn’t matter. This Samsung battery is rated at 800mAh, while the original Garmin was 750. So I should get a little more battery life.

It’s a little bigger than the Garmin battery, but it looks like it will fit, so I decide to go for it.

Preparing the Battery

After cutting off the plastic wrapper, we see the charging circuit on the top; the leads are flat metal strips that come around from either side of the battery.

IMG00062-20090815-1008 IMG00029-20090809-1656

After cutting the metal strips with snips, I determined the polarity with a voltmeter, and soldered a short wire to one side, to get closer to the original wires in the case. The flat lead strips look like steel, but they aren’t – it’s very easy to solder to them.

IMG00037-20090810-1851 IMG00040-20090810-1855

The case is the positive terminal, and the negative terminal is a pin that goes into the middle of the battery. I was careful with the existing insulation, and wrapped electrical tape around my little creation. There are exposed electronics and foil in the top of the Garmin (see the above picture.) I didn’t want any of this shorting to the battery case.

Installing the Battery

This starts simply enough – just solder the leads to the wires in the case. A short length of heat shrink tubing insulates the wire, and the exposed positive lead is so close to the battery it can’t go anywhere.

IMG00041-20090810-1902 IMG00043-20090810-1904

At this point I discovered something I hadn’t noticed earlier; there are a couple of little plastic pins molded into the bottom of the case, which prevented the old battery from moving around. I had to cut these with a sharp knife in order for my new battery to fit flush in the case. It’s a little wider than the original.

Red arrows point to the location of the left and right pins, which had to be cut. The green arrow is a bottom pin, for comparison; these can stay.

IMG00045-20090810-1907 IMG00044-20090810-1907 

The Moment of Truth

It fits! I pop the top on and power it up, and we’re looking good.

IMG00049-20090810-1910 IMG00048-20090810-1909

Sealing the Case

IMG00055-20090811-0757Now I just have to put it back together. The original adhesive is some kind yellow, slightly stretchy stuff. I’ve seen it before, but I don’t know what it is. After reading others’ posts, I decided to go with silicone adhesive, which I found at the auto store for a few bucks. We want a watertight seal, but nothing so permanent that we can’t reopen the case.

I applied a little to the edges of both the top and bottom of the case with a toothpick.

The whole thing is wrapped in a cocoon of tightly stretched electrical tape and left for a day. The edge came out looking pretty good.

IMG00056-20090811-0814  IMG00061-20090812-0750

I’ve been for a couple of runs and a bike ride, and it works just fine. The battery I put in it was used, and I haven’t tested the battery life. If or when that becomes an issue I’ll just buy a brand new battery, now that I know I can get one that will fit.

Update - 2010.05.12 

Ciccio and others note in the comments that the problem might be a short, rather than a bad battery. His advice is to check the battery with a voltmeter, which is of course a good idea. It might be good to clean the contacts between the front and back of the case, check for continuity where you can, and then reassemble and see if the battery charges. I like to clean contacts with a pencil eraser (the pink abrasive kind.) Here's a picture of Ciccio's fix for his bad contact:

Comments (98) -

2/7/2010 1:00:09 PM #


I was surprised that openening the case was so easy, closing made more trouble (because of the size of the new battery). I used an Uhu (I live in Germany) superglue as adhesive. I hope I can open it again in a few years ;-)
The battery Nokia BP-6M 1100mAh is quite thick, but it works fine when you remove the complete housing and isolate the top side only. Soldering the + pole was not that easy, you have to use additional flux.
1st time charching made no problem, tomorrow I will test is in a long run, I hope everything works fine ...


2/7/2010 1:00:09 PM #


How many years your battery lifetime was?


2/7/2010 1:00:09 PM #


genius! thanks for posting this


2/7/2010 1:00:09 PM #


Wow!!!!! I think maybe i ll do damages my garmin


2/7/2010 1:00:09 PM #


Super, I modified my battery. I had old Nokia BP-6M 1100mAh battery and it works fine.
Orginal battery has circuit but do not use it. Charging does't work with this circuit.


2/7/2010 1:00:09 PM #


It's not always the battery, I assumed it was and opend mine up to check it out but the battery was OK.
Problem was the unit wouldn't start without pressing mode + reset followed by the power button.

I lifted the internal watch contact strips to put a better connection between the two halves but that made no difference.
I found that I couldn't delete all the history and the watch had recently turned itself off on a run after giving a low battery warning => the history was corrupted and caused the watch grief.

The only way I found to delete the history was to load a v 2.80 (or earlier) version of the watch s/w (current 2.90 doesn't delete history and there is no tool to do it!)
Fortunately I had a copy of v2.80 but the old version is not now on the Garmin site (that I saw).
Moral of the story, don't run your battery low for two reasons, Li-ion batteries lose capacity if you run them below ~30% and also if the watch "low battery" turns off while recording it can corrupt the history and really upset the watch.

At least I now know how to open the watch and have found plenty of possible small mobile phone batteries that will fit (Samsung have a few possibilities). The ABSOLUTE max size of a replacement battery is 36mm H x 43 mm wide x 5.8 mm deep.
If you go 43 mm wide you have to trim a couple of internal plastic ridges in the case.

Good luck and try starting after pressing mode + reset if it won't fire up then try and delete all the history.
Also DON'T run the battery low if you want it to last, Li-ion work opposite to NiCad and NiMH which should be fully discharged before recharge. You try and keep them above 50%.



2/7/2010 1:00:09 PM #


GREAT Job!!! I was about to throw mine away. I'm not quite sure about the charging circuit beeing within the case. The original battery also has a little circuit on it. Is yours still charging and working fine?


2/7/2010 1:00:09 PM #


genius indeed!


3/4/2010 4:05:10 AM #


I have done the same modification as i suspect my battery is dead too. However after the mod, the problem persist. The symptom is like this; When the watch is in the cradle plug into the charger it will start and operate normally when i turn it on. The moment i remove power from it by removing from the cradle or turning off the charger, the watch will go dead. Nothing will turn it on unless i put external power thru it. Any idea out there? Anyone having the same problem?

I notice you have removed the small circuit board of your samsung new battery and not having problem. Does it mean the charging circuit is actually on the watch itself not on the battery? If this is the case I could have a dead charging circuit. Please comment on this idea.


hw Malaysia

3/4/2010 7:25:53 AM #


My 305 is still working perfectly six months later, and I use it (and charge it) almost every day. So I'm sure the charging circuit is in the 305, and not in the battery. If I didn't have a charging circuit, the battery would surely be fried after six months.

There could be something internally wrong with the charging board or chip, though that seems unlikely; those kinds of electronics are pretty bombproof. But if that's the case I don't know if it would be repairable. Maybe you could find a broken 205/305 on ebay for cheap, and use the back half of that case (with charger) and the front half of yours.

Or you might just have a broken wire, either running to the battery, a cracked wire on the board itself, or a bad solder connection on the board. I've seen this with microphone jacks on radios and stuff. If you have a voltmeter, see if you can find a bad connection. Good luck!

Jim United States

5/12/2010 6:52:02 AM #


Before changing the battery please check with a multimeter if it is really low!
I believe the battery was died but opening the unit I see with multimeter that the battery voltage was 4.04 V.
When I tried to recharge the battery the message was"Recharge completed" but the moment i remove power from it by removing from the cradle or turning off the charger, the watch will go dead.
The problem is that the first pin (on the buzzer side) was interruped so I use a flying wire and the watch works again.
In the same time I change the buzzer (you can find it in children's toys) and now the watch is already new !!!
I send the picture to Jim so he can put it on the blog.

ciccio Italy

5/13/2010 9:47:42 AM #


Hi ciccio,
I’ve the same problem with my garmin 305. I thought the problem was the battery but, as you did, I measured 4.04 V too.
So I hope Jim put the picture you sent on the blog as soon as possible.
Thanks to everyone.


Maurizio Italy

5/24/2010 4:42:17 AM #


Charging circuit sits on garmin battery, not on the unit.
should I remove charging circuit on the 800mAh from samsung, and not using any charging circuit ?

Roger Norway

5/26/2010 12:05:38 PM #


How long charge, do you allow it to stand while you're at work or overnight?
Do you leav it alone or controlled the charging with a clock?

Roger Norway

5/29/2010 12:50:53 PM #


It's been 10 months, and my 305 is still fine, with great battery life. I leave it on the charger for days at a time, with no battery problems. I disagree that the charging circuit is on the battery, as some commenters have said. There's a tiny breadboard on it, but I examined that and didn't find any circuitry on it. If I missed something, then it's redundant or unnecessary, because after 10 months of almost-daily use and charging, mine is fine.

Jim United States

5/29/2010 2:08:35 PM #


Because of a crash on my bike last week, my 305 was only working anymore via the cradle. I opened the device and noticed that that one of the contact strips was broken. But after assembling the device everthing was working fine but if I connected
the 305 to the computer the device was not recognised. I have tried a USB-driver update but that did not work.

Can the error be caused by the broken connector?

Steven Belgium

7/14/2010 1:36:36 AM #


Steven, my 305 stopped producing sounds after I dropped one too many times :( so I opened it up and I thought it was the connector problem. I used my multimeter to check which is the pin for the piezo and soldered wires from the piezo to the board directly. Alas it didn't work so I guess it was the something else broken inside.

Anyway, I believe the pins that connects to the USB, both + and -, might not be touching the board so it could be caused by the broken connector. You can bypass it by doing what I did for my piezo; soldering tiny wires on the back case's contacts to the front board. I can be done and I've done for all 8 pins; I got clumsy and broken the connectors one by one...

Let me know if you need help.

PS: Anyone having a loss of sound problem?

Winston Malaysia

9/18/2010 3:23:41 AM #


Thanks for the article, I changed the battery at my forerunner 305 yesterday. most difficult was to find the right battery, I used a mobile phone battery pack for Nokia, 9300/3250 3.7V 1000 mAh which fits perfectly. I had to remove a small circuit which was inside the battery pack. Not sure if it was a charging or a temperature controll. To be checked in the next days.  I'll test the device in the next days/weeks, right now -in lab env everything works perfect.

Martin Germany

10/16/2010 6:32:49 PM #


Hi, Just trying to follow these instructions and replace using a Nokia BP-6M LiPo battery.  Does anyone have any detailed instructions/pictures of how to dismantle the battery please ?

I understand that I hve to remove the small circuit board from this battery and solder directly to the foil/aluminium "arms" directly, is this correct ?

Thanks in advance

ASG United Kingdom

10/17/2010 11:24:53 PM #


I bought two Nokia BP-6M 1100mAh battery off ebay for ~ $4.00.

I took the paper/plastic wrapper off one of the batteries and popped the battery out of it's plastic frame. After attaching two wires, I wrapped it in insulating tape.  I did *not* remove the battery protection circuitry on the battery. I soldered  the wires directly onto what would be the normal battery +/- terminals. The modified battery fits in the 305's case and the unit works including charging.

Another happy customer! Thanks for all the tips.

Rich United States

10/19/2010 3:42:05 AM #


Hi Rich,
Thanks for the detailed reply.  
So you left the little circuit board in and soldered directly to +/- terminals of the battery.  Just to be clear the +/- terminals of the battery, do you mean the copper coloured pads that are on the topside of the battery that would make the connection if the battery was to be inserted  into a phone.....or where the foil from the inside of the  battery is brought out and attaches to the circuit board - one at either end of the little circuit board.

Thanks in advance.


ASG United Kingdom

10/19/2010 9:21:45 AM #


Yes, I left the circuit board in place and I soldered to the copper pads on the top of this board. These are the pads that would make connection to the phone. i.e. the circuit board is in place and still connected and used as it would be if the battery were used in a phone. There are three copper pads. From memory the outer two are + and -. This is clearly marked on the battery label/wrapper. Take a look before you pull the label/wrapper off.

The circuit board looks to be a protection circuit that prevents the battery from overcharging etc.

Rich United States

10/28/2010 10:00:13 AM #


Hi Rich,
I have a Garmin Forerunner 201 and there are four copper pads on the outside of the watch that connect to the charging cradle. Some of the copper pads are wearing off and the watch is no longer charging. I know if I replace the copper pads it will charge again, but I don't know where I can purchase copper pads. Any suggestions?

Thanks in advance!

texrunner United States

12/30/2010 11:35:34 AM #



I just bought a Nokia BP-6M battery but it does not fit in the 305's case... it is two thick. Any pictures or someone that can help me with dismanteling the battery?


Jose Spain

1/7/2011 10:17:05 AM #


No pictures, but the BP-6M will fit in a 305
1) Peel off the paper/plastic label that wraps the battery
2) Push the battery out off the plastic frame
3) After you have soldered the connections to the battery, wrap it in insulating tape before installing

Rich United States

1/23/2011 8:02:20 AM #


Just pressed mode rest and power and it turned on--thank you, i thought I might have to replace the battery. Will be using it today!

Don Canada

2/12/2011 4:11:37 PM #


If you can't get the case open and the Garmin works on the docking cradle then another option to replacing the battery is to use a battery powered USB re-charger, like Duracell My Pocket Charger, etc. See this site http://runtrails.net/garmin305.html

Jenny Australia

3/2/2011 5:11:41 PM #

Staffan Lindfors

Very helpful info! Thanks. My problem seems to be a open circuit on the little connector board.
The battery tests@4.05V after more than 4 years and 3-4 hours of usage every week. Since it is open, i will replace the battery anyway.
Still i can not find any +V on the 8 connector-pads. The negative line, i assume, is connected to  pad #4 & #7 counting from the left. I think, by looking at the printed board that V+ should show up on the first one from the left. Can anyone confirm or correct that?
Since the battery leads comes in on the downside, i suspect it is a double sided circuit board, and i have lost connection between the layers.
Comments anyone?

Staffan Lindfors Sweden

3/6/2011 3:22:28 PM #


Ive had my 305 for about 3 years and found today that it will not switch on and displays "charge complete" within seconds of putting on the dock. I tried the various resets without success.

I took theunit apart as you descibed and found that the battery was slightly swollen, a sure sign it's past it's best and quite possibly breaking the contact between the spring contacts and the contact pads.

I used a 3.7v 740mah battery from an olympus camera, type OL40, because it was spare, fairly new and fitted. I removed the battery protection circuit from the new battery and replaced it from the one on the original Garmin battery. I was able to re-solder the protection circuit on to the new cells tags.

So far so good. It all seems to be working as new.

A word of warning, lithium batteries, if mis-treated are dangerous. If you want to know how dangerous do a search on youtube. So for anyone contemplating this fix please pay attention to the polarity and be careful not to physically punture either the old one or the new one. If at all possible, re- use the battery protection circuit from the original Garmin battery.

John United Kingdom

3/20/2011 9:43:15 AM #

il bourgis

i have a garmin 305 . i have two problems today i have tried to push the button ON but it does not work ,when i connected it with the pc it works (the battery is completed ) but the pc doesn’t recognize the devise,so i can not transfer the data.please can you help me

il bourgis Greece

4/15/2011 8:13:38 PM #


Several people have commented on the difficulty finding replacement batteries.  let me suggest:


Once there, search their site for: Sanyo SL20 Li-ion 720mAh (BLI-244).  The cost is $9.44.  They ship via USPS and they usually ship same day.

The battery in in a grey plastic case.  I soldered and installed it as is.  If I replace another, I will remove the outer casing to save a little room.

Tony United States

5/3/2011 3:55:31 PM #

Gary Dennis

I thought I did exactly what you did but my unit will not power up. It worked before I started this so it must be me. I removed the small board attached to the battery. You did the same is that correct? Just red to the positive and black to the negative correct?


Gary Dennis United States

5/13/2011 3:34:51 AM #


I have the same problem :
>>The problem is that the first pin (on the buzzer side) was interruped so I use a flying wire and the watch works again.
In the same time I change the buzzer (you can find it in children's toys) and now the watch is already new !!! <<

Can you give me a small "how to" so I can fix it?

Thanks in Advance

Tarik Germany

5/27/2011 7:28:13 AM #


I tried using BL-6P nokia battery but couldnt get charging to work.
Must say, I took the circuit off.

raanan_t Israel

5/29/2011 5:18:31 AM #


Thanks for the great writeup.  Looks like I have my Garmin working again.  Here's my experience....

Be sure to try clearing the history before opening the unit.  I opened mine, checked the battery( which had a partial charge), cleaned contacts and still couldn't get it to work, even in the charger.  I re-read the posts again and saw the reference to clearing out the history.  Once I did that, everything started working.  So I am wondering whether all I really need to do was to clear the history or whether it was combination of clearing the history and something else.

Either way, I am happy to have it working again.  Thanks!

Lyle United States

6/5/2011 4:52:22 AM #

Luigi de Gaudenzi

I had the same problem, but mine can't be solved: the first contact of the array is oxidized! I can send you a picture if you want.


Luigi de Gaudenzi Germany

6/6/2011 3:16:08 AM #


Thanks Jim and Rich (for the nokia BP-6M suggestion - is a great fit and very easy)
My trusty 305 started playing up and would no longer charge at all. Opened it up and it was all OK inside...but no volts from the battery.  A little soldering and some silicone and I am back on track.

Alec Australia

7/2/2011 9:10:28 PM #


Pressing and holding mode and reset while turning it on fixed my problem.  Thanks to Steve.

Dan United States

7/3/2011 1:31:36 PM #


The fix that Ciccio mentioned worked for me. On the 205 that I've fixed, the 8th (from the cap, left to right) contact was oxidized and the link was interrupted.I had to  solder a shunt to re-make the link. After that the device was recognized by OS and I could charge it. The "Battery Charging COMPLETE" didn't show up immediately after I plugged the USB cable.

Catalin Romania

7/5/2011 4:30:08 AM #


I have a problem .... when new battery was empty, i tried to recharged it and no success....so i assume that new battery is not charging.... how can i solve this problem... is this a matter of battery or garmin itself ?? hmm
anyone hace similar experiences ??

GoZilla Slovenia

8/13/2011 11:30:11 PM #


To answer the Staffan 3/2/11.
The + (red) from the battery goes to the 8th connector on the little board
(and negative is #4 and #7)
On my friend's 305, the 8th contact was totally corroded and no longer
made connection from the + battery terminal to the board.
I cut the red battery wire and directly soldered it to the matching connector on the main board.

The watch had the same issue where it was saying "charge complete" within seconds
of being placed on the cradle and went dead immediately after being removed.

Staffan said:
"Still i can not find any +V on the 8 connector-pads. The negative line, i assume, is connected to  pad #4 & #7 counting from the left. I think, by looking at the printed board that V+ should show up on the first one from the left. Can anyone confirm or correct that? ..."

Chris United States

8/18/2011 1:31:13 AM #


My 305 connector pads were corroded too. I sent the watch to a cellphone repair shop and they replaced all the connectors and it worked like new. Repair cost usd30 to 40 for labour.

Hahn Malaysia

9/23/2011 10:00:27 PM #


Just tried the Nokia BP-6M with NO success. The one I received has an overcharge unit that adds a couple critical mm. I even tried to strip it out of the plastic casing the overcharge unit is melted into as a frame, but its still too big. Even if I got the shell closed again, I was concerned about the pressure I'd be putting on the boards and screen in the top part.

Happily the Garmin is unscathed so far, although I had to take it outside hooked to a laptop and the dock to test that, lol.

Going to Batteries Plus tomorrow to see if they have something slightly smaller now that I have the old Garmin battery yanked out and in hand...

heavyboots United States

10/6/2011 4:16:07 PM #


actualy i made it work ....
ordered samsung battery from ebay
.... go throught steps .... and voila :) ... just another problem occured .... GPS stopped working ... damn ... i guess it's those little contact issue :)

GoZilla United States

10/12/2011 7:15:58 AM #


My 305 can not locating satellites. what really happen and how to recovered it.

Ekkaphan Thailand

10/13/2011 3:10:26 PM #


Have just replaced the battery in my 305 with the Nokia  BP-6M. I had to strip off all the circuitry to get it to fit. I believe the little circuit attached to the Li-On battery is to protect against rapid DISCHARGE. So, once you remove this circuit, be careful not to short out the leads. Once it is installed and sealed, it should not be a problem..
The battery works fine, but like GoZilla, I am not getting satellites at all. At least it is a beautiful stop watch! Any hints for restoring the GPS function..
When I attach it to a USB on my computer. it charges OK but the computer doesn't acknowledge it.

Keith United States

10/19/2011 2:58:49 PM #


Thank you for the post!!!
It's was very usefull for me. Here in Spain is 80Euros to change the battery.
Moreover, you have a very very good page here.
Take care

Jose Spain

11/14/2011 11:21:59 PM #


I too found the Nokia BP-6M to be too big.  The battery I got had no plastic frame and the metal case was too big.   So the BP-6M was a no-go.

Instead, I found the Nokia BL-5X turned out to be a perfect fit.  The dimensions are 32.6 x 37.5 x 5.6 mm.  It's the same thickness, but about 1mm wider  and 1 mm shorter than the original.  It's was a perfect fit with no modification to the battery or need to strip off the protection circuit.  I nipped off the little pin that located the original battery , but I don't think I needed to.  I just soldered on the wires from the old battery, a little thin double sized tape on the back of the battery and glued the watch back together.   Double check the polarity on the battery with a meter as the generic battery I received had the polarity markings backwards.

I'm charging up the watch right now.  The new battery is rated at 600 mah versus the 720 marking on the original, so maybe I'll only get 8 hours instead of the original 10 hours.  Certainly much better than the 1 hr I was getting before I did surgery!  

For the guy that lost the GPS function, I wonder if the oversized 6M battery put too much pressure on the gps board.  That's exactly where it hit when I tried to fit it into my watch.

Chris United States

12/6/2011 6:53:41 PM #


Thanks for this Jim.
DBI9715A from Duracell direct which is a cheaper replacement for Samsung SLB-0837
I have used this battery, which fits nicely, only removing the bottom plate of the battery and one of the pins in the watch case.
Had to lengthen the red (+ve) wire a little.
the pads took solder OK.
My original battery (dated sept. 2009 was bulging too. I think this could be a safety issue with substandard batteries.

David United Kingdom

12/8/2011 12:54:46 AM #


Forgot to say battery is rated 820mah.
First conditioning cycle gave 14 hrs battery life with outdoor use selected

David United Kingdom

12/19/2011 4:48:07 AM #


Hi Jim!

This is awesome! I replaced the defective battery with a Sony Ericsson BST-37 and used a silicone glue of the brand "UHU". It works perfectly up to now. I posted the whole procedure on our triathlon club's blog (in german):




Harald Austria

12/22/2011 7:01:39 AM #

J&#248;rgen Bo Madsen

Many thanks for this very valuable guidance. I followed your instructions and my Forrunner are now as good as new!
Kind regards
Jørgen Bo Madsen

Jørgen Bo Madsen Denmark

1/28/2012 4:22:37 AM #


Once there, search their site for: Sanyo SL20 Li-ion 720mAh (BLI-244).  The cost is $9.44.  They ship via USPS and they usually ship same day. http://www.androidactivesync.com. The watch had the same issue where it was saying "charge complete" within seconds
of being placed on the cradle and went dead immediately after being removed.

Rudy United States

2/9/2012 10:29:28 AM #


Awesome post - thank you for the excellent instructions.  My Forerunner 305 wouldn't power on anymore due to a dead battery.  I bought the same battery brand new on Amazon for $4 - so much better than the $75 and 4-6 weeks Garmin wanted to fix it!  Thanks again!

Dave United States

2/15/2012 2:12:49 PM #

Josep M

Nice post!
i will try to replace the battery for one with 2250mAh.
There's a Nokia BP-6M compatible that has 2250mAh.
Anyone has tried this? I think must be no problem. Please tell me if someone thinks this could be a problem for some reasen
I will tell here if it success and if my 305 gets double duration.
Thank you!

Josep M Spain

2/16/2012 1:37:52 PM #

Josep M

nice post.
I will try to do the battery replacement with one compatible Nokia BL-5X that has 2430mAH (x3 than the garmin original).
I expect to get double time duration on my 305.
I think that must be no problem, but, someone has tried this? Do you think can go wrong?
Thank you!

Josep M Spain

4/6/2012 7:45:33 AM #

Brad Bishop

I offer a repair service on eBay to replace the Garmin 305 battery and and a repair service.  I use a 3.7V 1400 mAh battery that provides double the run time of the stock Garmin battery.  The most common problem is corrosion of the 1st connector PIN.  This PIN brings in the positive power from the battery, when it goes your Garmin will not power up on its own, however will still power up in the cradle; (the 4th contact on the bottom of the cradle brings positive power in from the cradle which bypasses the battery).  Sometimes a new PIN can be soldered to the main board, however if the corrosion has eaten away all the contact surface on the main board then there is no connective surface to attach the new PIN.  In this case I run a bypass wire from the positive battery lead to the proper connection point on the back of the main board.  Before you spend your money on the Garmin repalcement service you may want to try the repair yourself; if your unit is within its warrentee period please have Garmin fix it.  If you would like me to fix it you can find me on eBay, I only charge $25.  Good Luck! Brad

Brad Bishop Canada

4/9/2012 6:25:03 PM #

Adam Engst

I just went through this replacement with my 305, and I wanted to add a few bits of advice. First, mine was extremely difficult to open. The spots others have mentioned prying with fingernails didn't respond even to knife blades. Eventually, I was able to wedge a thin knife blade between the two halves of the case at the bottom, under the Garmin logo. Then it popped off quite easily.

Acquiring a replacement battery was also a major problem - most of the batteries others have recommended were no longer available. However, I found a mention that the iPod mini battery was roughly the same size, and those are readily available on Amazon. I bought this 1300 mAh battery for $4:


As far as installation goes, I'm not experienced with soldering, but I was still able to desolder (with wick) the leads from the old battery and from the iPod mini battery and (with help from my son, who had to hold everything in place carefully) solder the Garmin's leads to the appropriate spots on the iPod mini battery. I did have to trim off that little plastic peg someone else mentioned.

Obviously, 1300 mAh is way larger than the 750 mAh battery that was in there, but it's also a cheap battery and I don't have a sense of its quality. I've used the 305 for a couple of runs since, going well beyond the point where the old battery would give out, and I also left the watch on for 6 hours - it was still on at the end, though the battery warning dialog had appeared.

Not trivially easy, but well worth it for avoiding the $79 fee from Garmin.

cheers... -Adam

Adam Engst United States

4/10/2012 12:37:32 AM #


Very impressive!
  My GARMIN 305 turns off every time I touch a button or while riding.
There may be a loose contact of the battery?

Good day

shaul Israel

4/18/2012 12:58:43 PM #


I also had the problem my battery had very little uptime (about 1 hour) and now it also stopped working on its own. It worked only on the cradle.(problem has been mentioned before. I opened the 305 and found the 2 contacts on the right side completely destroyed. I could not attach a wire to the bottom of the watch (on the little circuit board) so I did some measuring and I soldered the 2 wires from the 2 contacts(last contact to the red wire or + and the one in front of this to the black one or -) to the contacts (parralel) on the battery. I also replaced the battery with the Nokia BP-6M  accu. I did a test and after everything looked well I glued it together and hope it will work for another 5 years! After all it's no big deal!

erik Belgium

4/20/2012 5:57:14 PM #


I found a quicker battery for replacement,  a Rayovac Model # CAM 10561

Bill United States

4/26/2012 8:13:51 PM #


For those wondering if they can remove the tiny circuit board (PCB) on the battery:
The answer is yes, sort of.
The PCB on the battery performs temperature sensing information (which the garmins don't support, so no loss there) and low-voltage cutoff (they cut the current when the battery voltage drops to 3 V).  The low-voltage cutoff feature is important, because it means your garmin will just die when the voltage gets low, instead of continuing to draw current from the battery.  If the battery is drawn down below 3 V, then irreversible damage is rapidly done to the battery, _drastically_ shortening its life.
If you always keep the thing well charged, then there's no issue, but if you tend to run it down to the bitter end, then you'll want to keep the thing attached.

Also, for what it's worth, newer versions of this battery have a plastic insert between the battery and the PCB.  If you remove this (you need to for the 305, as it takes up too much room), then be sure to put a piece of electrical tape between the negative lead and the battery case (the whole case is the positive lead - no tape = short circuit!).

Kevin United States

5/16/2012 7:27:48 AM #

Luis Otavio

dear sirs

I am having the same problem with my garmim. the attery popped.
please, which model of samsung battery did you use to fix your garmim? please, inform the model of the cell phone to me. I willl look for the battery.
your explanation was fantastic.
thank you in advance.
best regards.

Luis Otavio Brazil

5/27/2012 10:44:11 AM #


This is a great thread, thanks for posting this.  I bought a cheap imitation of the SLB-0837 on eBay, and I'm about to replace my Garmin 305 battery with this, but I'm wondering what to do with the third battery terminal marked "T".  Anybody know?  Thanks.

scott United States

5/29/2012 3:56:23 AM #

Ton Koenraadt

One question that comes up when reading all these valauble replies, it is not clear to me whether this small circuit protecting the battery from overload etc. is removed? I got the impression in case of the iPod Mini  and the Durcacell it was not?
@Kevin and @Jim, does it harm to leave this circuit on and directly solder on the battery pads?


Ton Koenraadt Netherlands

6/5/2012 5:17:30 PM #

Ton Koenraadt


Replaced the battery with A TomTom one @ 1340mAh.
Starts up fine, but my "mode" button doesn't work anymore. I'm sure I did not damage the print board or switch nor rubber button on case.
All rest works as well e.g. start/stop, cadence and heart rate sensors.
Any suggestions in getting this working again?
BTW, pressing mode and reste simultaneaously didn't fix it either.

Ton Koenraadt Netherlands

6/6/2012 2:14:34 PM #


Hey all,

I ran into the same issue of the final connector pin corroding and my 305 turning off at very bump, I was planning to replace the pin and be on my merry way when I noticed that I now can't power the unit on or get the charging screen even when sitting in the cradle with the two halves pressed tightly together.

Based on Brad's post I assume something new is wrong since the cradle should be bypassing the corroded pin.

Any ideas?


Sesh United States

6/10/2012 3:10:29 PM #

Mike C

I think I may have found a useful and easy solution. I went to Amazon,
and bought a battery which not only works, but fits perfectly: "NEW 1300mAh BATTERY Compatible With iPod® MINI 4GB 6GB." No modifications are needed at all. I soldered the wires together, covered the solder joints with a bit of heatsink and put a drop of rubber cement under the battery to hold it in place. You can cut off the white wire, it is not needed.

I also used rubber cement to snap the top back and held it in place with some strong elastic bands until the glue set. This will also waterproof the case from rain, sweat, etc.

The battery costs $0.64 , yes, sixty four cents brand new in the packet! (plus shipping),  and seems to be a very good solution. My 305 is back with me on the road.

Mike C United States

6/10/2012 7:55:47 PM #


Steve you just saved me from a big headach and a trip to the store.  I was sure my battery was dead and was expecting a nice bill with it. But your mode + reset followed by power worked!!! 1000 thank you :)


Tracy Canada

6/26/2012 8:52:07 PM #


Samsung SLB-0837 1100 mAh ($7 amazon) almost fits, only one pin to remove. I left the battery plastic case intact  and ignored the T terminal.  The red wire soldered onto the +ve terminal and the black wire onto the -ve terminal.  The +ve red wire had to be lenthened, just solder on about a 1" length of thin copper wire. The case took a little pressure to open, (from off, hold reset and power until screen instruction appears, then follow the commands) it but it went back together with silicone adhesive just fine. I did do the reset before I took the case apart. It seems to be working just fine.  Although the battery fits snug, I added a little silicon adhesive under the new battery - just like the original. I checked after about 4 hours of charging and the 'charging complete' was displayed.
Thank you everyone for your really good  info. I'll add a note if the 305 fails in the next littlel while.

Paul Canada

7/7/2012 8:50:02 AM #

Roberto Katalinic

Thank you Jim,

Another rescued FR305 here with a Nokia BPM6/M battery which is an absolutely perfect fit.


Roberto Katalinic United Kingdom

7/12/2012 6:02:21 AM #

Derek Brabrook

The circuitry on all Li-on batteries is the battery's protection circuit it purely monitors voltage and if that voltage drops below 3.07v (ish per cell) it shuts off current supply from the battery....it is NOT the battery charging circuit.... if battery drain continues below 3.07 volts it will eventually put the battery into sleep mode (completely disconnects the battery from supply for safety reasons) if the voltage drops below 2.70 volts, then below this voltage copper shunts can form effectively shorting the battery causing it to either detonate when charging or violently vent at some point with a pretty spectacular flame which of course is toxic.....

Most Li-on batteries also have a pressure vent/valve which will open circuit the battery if it goes above 200 psi or 500 psi in some .... (yes that pounds per square inch)

So to all those who have disconnected the protection circuitry you'll be ok (ish) as long as you keep the battery charged above 3.0 volts.

Things to look out for are as follows

A) if you notice your Garmin getting overly warm when being charged or when being worn then I'd start to think about changing the battery and in the latter case removing it from your wrist.....
B)  when you change batteries leave the protection circuit in situ if you can......

Hope that clears up a few points :)

Derek Brabrook United Kingdom

7/16/2012 11:05:24 AM #

O. Morais

Hi Brad Bishop
My 305 is "dead"!!! I opened the 305 and found the 8th contact from the base (on the little circuit board) had disappeared (that's it... There are 7 gold contacts and the 8th is gone...!!!. There are no contact at all!!!). On the main (top) the 1st and the 8th pin contacts are also broken. What do you think that i can do? Do you think that it could be fixed?

O. Morais Portugal

7/17/2012 9:09:25 AM #

O. Morais

Hi all... can anyone post the "function" of the contacts and the pins? I'm confused... when saying "the 8th contact from the left", means that the 1st one is the closest to the little screw on the base (where the battery is)? And the pins? The 1st one is the closest to the little screw on the top (where is the GPS...)? This one connects to the 8th contact... Is that right?

O. Morais Portugal

7/24/2012 5:39:12 PM #


I've had this Garmin 305 for 4+ years and three times now I resurrected this Lazarus. I discovered that the "lap" button was sticking. I think what happens is that sweat gets in and causes the button to stick and drain the battery down to zero. So, my technique is to wet a cotton swab with water and try to work it in around the sticky switch. I work the switch until it has the same sound and travel as the "start/stop" switch. Then I do a soft reset (3 seconds holding mode and on/off down), put it in the charging cradle and wait. What has happen all three times is that the "Battery Charging in Progress" window doesn't come up immediately. I go on to something else and look over in a few minutes and it's charging. Yippee. Too expensive to replace.

Tom United States

8/12/2012 1:12:22 PM #


Just fixed my Garmin 305 with the help of this post.  The problem was just corrosion on the first two contacts.  It was very obvious, very visible.  I cleaned them with a pencil eraser and also sandpaper.  The contact that has the bend in it actually corroded right through so I bent what was left hoping it would provide enough contact.  For now it is working fine.  Can't believe Garmin doesn't give a free repair for such a design flaw.

Dnc Canada

8/24/2012 7:58:33 AM #

Steve E.

Replaced my Garmin 205 battery thanks to this site.  It's the same the 305 uses.  I bought the one Mike C. recommended on his post from 6/10/12.  This site helped me visually (I can't read German):
Have the following on hand:  Utility Knife Blade, Extra Blade (or Small Screwdriver), Needle Nose Pliers, Soldering Materials, Magnifying Glass,  Small Vice or extra set of hands, Clothes Pins, and Adhesive Sealant.
It's hard to open the watch without first running the blade all around the seam to remove the old sealant.  The extra blade will help you pry it open (do it from the Garmin Logo end where the watch band attaches).  If you open it from the side you might damage a button!  After it's open it's difficult to remove the old sealant from the grooves but it's necessary so it closes up again tight.  I had to snip the small tab so the battery would lay in place flat.  The battery is excellent because you only have to solder wire to wire.  No - I didn't open the battery or modify it in any way before I installed it.  The white wire can be cut away.  Red to red, Black to black.  Before you close it up make sure the battery has a good amount of adhesive to hold it in place.  Also make sure that you apply adequate sealant to the area of the watch where the watch band attaches (the opposite end from where you pried it open).  It's the area of the watch where the charging connectors are.  That area has to be super tight and well closed or the watch will not turn on or charge.  The clothes pins worked really well for me holding everything tight until dry (overnight).  The watch is very easy to close up and difficult to open.  It's probably a 2 hour repair with all your tools ready.  Everything on my watch works.  I used it 14 hours after the repair.

Steve E. United States

8/24/2012 10:14:12 AM #

Steve E.

Fixed my Garmin 205 yesterday.  Same battery as the 305.  Great website. Thanks  Mike C. (6/10/12 post) and, Harald (12/19/11 post).  I can't read German but Harald's website helped me a great deal visualizing the repair:
http://perpetuum-mobile-triathlon.blogspot.com/      Mike C. found the perfect battery ( I think I paid $3.65 for it including shipping on EBAY).  The battery has it's own wires so I soldered red to red and black to black and cut off the white wire entirely.  I did not modify the battery in any way except to cut away the white wire and the ipod connector.  I did however have to snip off the plastic tab so that the battery would lay flat as Harald's picture shows.  The hardest part was opening the unit.  You have to go around the entire edge with a utility knife blade to remove the whitish sealant.  Then you have to lift it up with the blade while you pry with a flat edge knife or screwdriver.  I spent lots of time cleaning the old sealant out of the groove in the two halves so that it would seal up tightly again.  Other than that it was pretty straight forward.  You should open the unit below the Garmin logo where the watch strap connects.  To do otherwise would risk damage to side buttons.  You also have better leverage there.  Make sure extra adhesive is used to secure the battery in place and apply a good deal on the other end above the display where the other watch strap attaches.  This is where the charging connectors are and it needs to be glued well and held very tight while drying (the clothes pins were perfect) or the unit will not charge or turn on.      Make sure you have someone help you or you'll have to have one of those clamp stands to hold the wires when it's time to solder.  What you need on hand:  Soldering materials, wire cutter, needle nose pliers, clamp/stand (or extra person), utility knife blade, small screwdriver (or prying device like butter knife), adhesive caulk (your preference), 5 or 6 clothes pins and a magnifying glass. It's a 2 hour job +/-    All my buttons and watch work perfectly.  I dried it for 12 hours and it works great.  

Steve E. United States

9/13/2012 6:30:12 AM #


I have to hold the watch in place on the charging cradle with elastic bands. When it says "battery charging complete" I take it out and try to use it, it immediately says "battery low". Is it the battery, or the cradle? Has anyone else run into this?
This thread is extremely helpful, although I have neither the technical expertise, nor the dexterity to make use of the suggestions contained.

billmathers Canada

9/17/2012 10:15:57 AM #


Response to:  billmathers

My brother's watch (Forerunner 205) was doing something similar.  When you have to hold the watch very tightly above the display area for it to work it probably means that you have a bad contact.  After replacing my watch battery above I repaired my brother's "dead" Garmin 205.  He sent it to me already open and you could see the bad contact.  I had to solder a wire like the picture shows on the main page above sent in by ciccio.   I found it best to use only a small amount of solder or it would prevent the other contacts which were not damaged from connecting once the watch was closed again.  After soldering it and resoldering it with less solder it worked fine.  If you don't have the dexterity for the job, maybe you could look into having someone like Brad Bishop do the repair for you.  He posted on 4/6/12 that he has a repair service listed on Ebay.

Steve United States

10/2/2012 9:31:54 AM #


It also succeded here to replace the battery in Forerunner 305 with Nokia BP-6M. I have chosen it as the most mentioned battery here in the post. Three important note:
1. This battery is a bit big. Maybe a smaller one can be  installed more simple.
2. The re-soldering of the + pole was not too easy. I had to retry soldering to get proper contact (measured by voltmeter at the most right two pins from the eight on the top!!!).
3. I removed the circuit from the battery (a slaughter-work). It is against over-heating, overcharging and overvoltage. After the first charge the watch screen output changed from '... in progress' to '... complete. So, at least the charge is controlled by the watch itself!

Thanks for all of you for the remarkable post. Zsolt

Zsolt Hungary

11/21/2012 3:15:31 PM #


Just to say, thanks for the guide. You can get battery with over 3x the original capacity if you get one of these: www.amazon.co.uk/.../ref=oh_details_o01_s00_i00 Its easy enough to solder the wires directly to the battery terminals. I left the protection circuit on the replacement battery, all seems fine. Even when this battery gets old and has less capacity, it will still be better than the original.

Richard United Kingdom

12/9/2012 4:55:46 PM #


Need help

I dropt my Garmin 305.  The 2 parts came apart.  It continued to work for a while after I put them back togheter but sometime it stoped working when I hit bump.  Now it is dead.  I can not see anything on the screen.  I tried to clean the connector, I tried the reset process and nothing worked.  Any suggestions?

Michel Canada

1/6/2013 8:54:55 PM #


Qualified success. Replaced battery in my 3 year old Garmin 305.  Pretty short life span, especially considering it never got wet.  No sign of water within.  Orderd battery from "eForCity" via eBay, cost about $6 shipped to Canada.

ISSUE #1 --- Be VERY careful which direction you pry it open.  I pried mine apart starting at the "bottom" (the red band under the word GARMIN) and hinged it at the top (above the display).  Doing so bent three of the little copper spring clips that connect the top half of the clamshell to copper pads on the circuit board.  It was real hard to get them re-aligned so the unit would boot up when the clamshelll was closed again.  Word to the wise: start at the top end, work toward the bottom, don't allow the top half to pivot or slide downwards on the bottom part.

ISSUE #2 --- the replacement battery has three wire connection leads: Black (-), Red (+) and White which is a thermistor for high temperature protection of the battery.  It's a little un-nerving reading the stories of Li-ion batteries exploding.  I don't intend to leave it plugged in charging unattended for long periods of time.

energizer0_0 Canada

1/9/2013 8:54:05 PM #


I finished my battery change a day ago and ran with my newly charged 305!  I used the 1300mAh noted above for an Ipod.  It cost $4.00!  The heat shrink tubing I was out of cost more than that! $6.00.  Thank you for posting the procedures Jim Rogers!

Jeff United States

1/24/2013 1:46:39 AM #


To Josep M.
Did you eventually tried the Nokia BL-5X with 2430mAH? How did it work? Please let us know.
Thank you.

Daniel Argentina

1/24/2013 1:48:39 AM #


Dear Josep or anyone else: Do you remember the dimensions of the Nokia BL-5X with 2430mAH?
Thanks again.

Daniel Argentina

1/30/2013 2:23:29 PM #


Thanks for this info. It was extremely helpful. I just successfully replaced the battery in my Garmin forerunner 305. The battery that I used was bought online from "Deal Extreme" and was a camera battery rated at 700 mAh, which was the Olympus LI-70B, for $5. I didn't have to take the case off of it, but I removed one of the plastic "pins" in the case. I just posted my experiences and a link to this "tutorial" in Hebrew on a local running/ triathlon forum.

Hermon Israel

2/19/2013 2:48:04 PM #

Josep M

hi! sorry i forgot to tell you,
the Nokia BL-5X its working ok.
But it didn't improve the batery duration.
I get about 10 hours of working, the same as the garmin original 305.
Maybe the forerunner 305 stops batery charging.
So you can use the Nokia BL-5X, but 700mAH is enough.
sorry i don't remember the size, but it fits perfectly on 305.
Now my 305 is nearly dead (battery ok), but the buttons are disapearing and not working....   :-(

Josep M Spain

3/20/2013 7:15:35 AM #

Wieśka F.

Usefull info, thanks man!

Wieśka F. Poland

3/27/2013 8:59:41 AM #

Lance Benn

Thanks for the article, Mine was dead, I opened it and the battery seemed fine, all I did was pulled the tabs between the two boards up a bit and reassembled, works great!!

Lance Benn South Africa

4/5/2013 6:51:50 AM #

Russ Keith

I replaced my battery in October of 2012 using this tutorial. I did it only a few days before running my marathon so I was a little worried about something coming loose. It is now April of 2013 and it still works as good as new!

With the new battery (1300mAh for an Ipod) and a soldering iron the cost of replacing my battery was less than $20 and I get to keep the soldering iron.


Russ Keith United States

4/16/2013 3:13:50 AM #

Colin Jenkins

Any tips for investigating a dead Garmin Forerunner 201? I can see any obvious way of getting the case open without resorting to extreme violence!!



Grewat, informative thread btw

Colin Jenkins United Kingdom

5/17/2013 10:50:07 PM #


Great post. My 305 was doing what a lot of other posters mentioned; it would say "batter charging complete" but when it's taken out of the charger, the 305 wouldn't function because of a "low battery".  I bought a battery at BatteriesPlus (they had actual replacement batteries for the 305).

However, after installing the new battery, mine still has the same problem. I didn't take the "charging circuit" (shown in the 5th picture above) off the old battery. Should I have done that? It's not clear how that's done or how to attach it to the new battery. Can someone comment, please? maybe w/ pics?

Thanks, Bill

Bill United States

5/22/2013 4:57:03 PM #

Mickey Cashen

Two comments:
Opening the case: see this website, also about replacing the 305 battery, on opening with fingernails: reedercommons.blogspot.com/.../...305-battery.html

My guess is that if fingernails aren't enough, a thin knife followed gently by a small screwdriver will pop it open without more than a scratch or two to the finish.

The same website used an iPod Mini battery (1300 mAh) bought for $4+ on eBay.

I hadn't used my My Forerunner 305 for a year, got back to cycling in April (a month plus) and the battery doesn't want to last much more than 2 hours.  Since I'm charging it on an often-asleep laptop USB port now instead of the always-on desktop I used to use, I may be doing something wrong, but the watch does reach the point "Battery Charging Complete" so I'm guessing I'm going to have to replace the battery.

Mickey Cashen United States

6/11/2013 3:40:49 PM #


I have changed the battery in my Garmin 305. However, only the garmin turns on its base when charging and not without it. That was wrong above with your original battery. To put it in its cradle, to get the message 5 seconds charging completed. They need help, please.

Alberto Spain

6/24/2013 8:30:51 AM #

Steve E.

I posted on 8/24/2012.  Both Forerunner 205's are still going great!  No issues with overheating (I cut away the white wire on the ipod mini 1300mAh battery for both repairs).  They never shut off due to battery charge even on the longest runs.  Thanks for a great website.  I'll be repairing a friend's Forerunner with the same battery and I'll update this website with the results.  It should cost about $5 for the repair.

Steve E. United States

6/25/2013 5:29:29 AM #

Steve E.

Just finished my 3rd Forerunner 205 battery replacement.  Success!  Using a wide razor blade scraper like the one you would use to take a bumper sticker off your glass worked great to help pry it open from the Garmin Logo side where the watch strap attaches.  When you pry it up you need someone to stick something small into the crack because it opens up and then closes right away when you take the pressure off.  I had my wife stick a small plastic disposable knife blade in there and then pried it open with my fingertips.  The watch opens like you are taking a bottle cap off with a bottle cap remover.  It lifts up completely from the side you are opening and lastly from the other watch strap end.  It's amazing how some watches come from the factory with a lot of glue between the two surfaces and some have very little.  In this case I didn't have to scrape off any glue or run my blade around the two halves before opening it (definitely made for an easier repair!).  The watch battery I use is ideal!  It's designed for the "ipod Mini" but it is ideal for the Garmin in my opinion:  3.7V 1300mAh.  You can find it for $5.00 or less with free shipping and a couple of small screwdrivers included if you search long enough for it on Google.  Then you are only attaching black wire to black wire and red to red (cut away the white wire... it's not necessary).  This replacement battery will last longer with a charge too because the one from the factory is typically only 720 mAh. The first two watches have been in service now almost a year with no problems.  I leave mine plugged in constantly to the wall outlet or the computer when I'm not running.  No issues - no overheating - no problems whatsoever.  I hope this helps you.

Steve E. United States

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