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.
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.
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In desperation, I decided to take apart the battery in my old Samsung Hue phone, which was sitting around, having been replaced by a Blackberry.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.
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.
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.
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.
The Moment of Truth
It fits! I pop the top on and power it up, and we’re looking good.
Sealing the Case
Now 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.
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: