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.

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. :)

Hola,

I figured at somepoint someone would have a similar problem. I´m no Electric Engineer but I know the battery is a lithium polymer battery. From playing with drones and electric skateboards I know that the standard "nominal" voltage of Lipo batteries in the 3.7V and they should only be charged up to 4.2 V and to extend battery life (at least with my electric skateboards) should not be discharged past around 3.5V. I assume the PCB will take care of the battery charge and discharge. I havent torn into the battery to look at the PCB yet. I´ll post some photos when I get there.

I was curious where you found the small lipo - 10mm x 20mm x 2.5mm cells???? I have been unsuccessful finding replacements based on the product code as well. I did fond some small lipos for older fitbit models. Ususally with lipos this small the batteries are sold with a PCB built in (again from my experience with smaller drones, and I was hoping to find something like that.