Sorry for the late reply to this, I've been very busy lately and haven't been able to check into WW.
So what's happening with your battery is basically a battery failure due to age, not necessarily the firmware or the device. When Li-Ion batteries die or get old towards failure, they will often give incorrect power outputs that are read by the device as 100% (even though this isn't the case). When I was researching this battery replacement thing, reading up on Li-Ion batteries and so forth, I did read about this occurrence. A similar thing happened with my laptop when the battery was past age.
As for re-calibrating battery settings on the Garmin? Nope, not necessary, it's been working fabulously.
I really wish a total expert in electricity/power/batteries would chime in here, but from what I understand despite the new battery having slightly less capacity compared to original, it is also operating at a slightly lower power, therefore it will be able to power the Garmin with the same battery life as the original. The Garmin hasn't shown any weaknesses or decrease in functionality operating at the slightly lower power... it's almost as if Garmin could have initially powered the unit with a lower power battery from the start.
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