OscarooYes I agree.
I've also had this issue. Its very frustrating.
Until this phone, accubattery has been perfect. In this phone the implementation of the battery API or power consumption whatever is shit and inaccurate.
After two 0 to 100 cycles I managed to get accubattery reporting up to 3500mah capacity.
Maybe with more cycles I can get to 4000mah but hen after two more 20 to 80 cycles it dropped down to 3300. With some weeeeird values at night when not using the phone. See screenshot.
Clearly, my phone can't drop 1% of charge and also charge up by 3563 mAh in 28 minutes
So... I'm just going to uninstall accubattery as it's worthless on this phone. Its literally useless and causes more heartache than anything.