Garmin's Forerunner 55 Battery Replacement, is it possible?

In theory it should be possible, but just by what I can find on it online it’s going to be difficult to replace. Just by looking at the device I can already tell you’re going to need an opening pick and maybe a heated device to soften any glue holding the screen in place.

Although, assuming that you can get into the device then you’ll need to find a replacement battery. I couldn’t find a new one online, but I’d be willing to bet if you contacted Garmin’s support they would put you into contact with their battery supplier. Otherwise you could maybe cannibalize an old Garmin for its battery.