I have been using my Garmin Forerunner 305 sportswatch for several years now, and it was not too surprising that the rechargable LiIon battery of the device finally reached the end of its lifetime. What I did find surprising, however, was that Garmin was not willing / able to offer a feasible solution to my broken battery problem, but rather offered me a slight discount on exchanging / upgrading my Forerunner watch to the latest model.

Well, I wanted to save the >150 Euros and exchanged the battery myself. Since the Forerunner is glued shut, I hesitated a little, but there are tons of descriptions on the web (and on Youtube) on how to exchange a battery on Forerunner watches. I bought a replacement battery from Amazon and followed the recommendation "People who bought that battery also bought this glue". For altogether 12 Euros I had everything that I needed. Fixing the watch was a cakewalk: I carefully pried the watch open, cut the cables to the battery, soldered the new battery in (using shrink-tape to cover the solder joints) and - just as a precaution - cleaned all contacts with an eraser. I then carefully glued the watch shut again. After 24 hours the glue was cured and I could charge the battery. I measured an impressive improvement of battery lifetime from 15 minutes (old battery) back to >10 hours (new battery). These were well invested 12 Euros plus 25 minutes of work. By now I have been running about 200 km with the repaired watch, both through sunshine and rain. The watch still works, which means that the glue indeed sealed the casing properly.

As always: If you try to do the same to your running watch and screw up, don't come crying to me. A user replacement of the battery is not intended by the manufacturer and you might damage the watch irrepairably. Also, LiIon batteries are dangerous and might catch fire or explode if not treated properly.