Charge value of the XZ1 is always 20%

[DG_WOL_KIRN]

Hello together,

I got a refurbished XZ1 Smartphone and the function is so far ok, nothing to complain, but the charge value is always 20%. It never increases or decreases, no matter if I charge it or not.

The phone is charging, I can see it when I installed  a battery monitor the voltage increases from 3.5V to over 4.3V and is alive for two days. But the charging value of the phone never changes, always it shows 20%. The same when the smartphone charge decreases, suddenly the phone switches off when the capacity is over, but the charge value always is 20%.

This is bad, as some updates needs a minimum charge value of for example 50%. And I have to watch the voltage of the battery to guess when it has to be charged.

Does anyone has an idea how I can change this, clear the charge value? Is there a damage inside? Is there a simple solution?

Thanks.