It seems there are probably 3 posibilities:
- the battery is defect
- the FP3 is defect
- only the FP3 Interface to the battery is defect
It could be good, if you could have the posibility to try the battery in other FP3,
just in case there is another one around.
By the way, do you know, if the battery of FP2 is the same for FP3?
I suppose not, just because of the different dimensions, but who knows,
just in case you have a FP2 around if not a FP3.