The value of charging the phone changes, it turns itself off, what's the problem?

Question

Mobile devices

I have an android phone, so let's say it has a charge of 80% percent and the phone used to turn off abruptly, and when I turned on the charge back, it wrote 2 or 5% differently little or at zero. And it also happened that I rebooted 3 times and the batteries became as much as it was, that is, 80%. What is the reason in the phone or in the battery?

Answer 1

Battery charge controller. Take it to service

Answer 2

Try a different battery.
If nothing changes, then the problem is in the phone.
Works as it should - throw out the old battery.
And if the battery is non-removable, contact the workshop.
Also, as an option, you can try resetting the phone, saving all the important information from it to the computer before that, and contacts to the SIM card.
There are also glitches in phones due to the fault of a SIM card or a memory card - try inserting it from another phone.