In the menu, how big does it say your battery is?
According to the specs, FP3 is supposed to have a 3000mAh battery. The phone itself however claims it has a 2000mAh battery:
( read out with app “CPU Info” from Fdroid )
however in “About Phone” in the settings menu it claims the battery tyype is 3060 mAh.
i dimly remember seeing 2000mAh somewhere else, maybe while browsing sysfs in adb
/sys/class/power_supply/…