I did some more searching, lipo batteries in this voltage are usually labelled as "3.7V" meaning they are a cell with protection pcb that operates up to 4.2v (full charge) down to 3.2V (discharged).
The battery cell in mine measure approx 12mm x 18mm x 2.5mm (WxHxT); with the proection pcb it was a total of about 12mm x 22mm x 2.5mm.
I ahve not found an exact replacement, but did find 10mm x 20mm x 2.5mm cells which should fit... going to order some and see if a bit of soldering will ahve a better running fitbit. :)
The band on mine fell apart but I already had one sent for warranty. Min still worked so I took it apart, and while trying to look for a replacement lipo (Searching the number on the battery) i came here... The batter is measuring between 4.1 and 4.2v. There appears to be some sort of protection or charging board taped to the lipo that I think we need to keep if we are to replace the lipo battery.
Lorsqu'il en aura reçu, il pourra afficher un graphique de sa réputation au fil du temps.
Voici un aperçu de ce à quoi ressemble ce graphique :
Aucun point de réputation obtenu pour l'instant.