Possible reasons are as follows:
1, the time used is too long, reached the charge and discharge cycle, should be replaced with a new battery.
2, the purchase of inferior battery cells made of batteries, it is easy to internal short circuit display a full charge, but there is no electricity; Or damage can not be identified and charged.
3, the charging method problem, you see whether the direct charge contact sheet and the battery correctly contact, change the position (there are several contacts on the battery, try it in pairs), or press (some move) the transfer switch on the charger, it may be done
My p20 is fine... The sudden failure to enter the electricity may be the following problems:
One is the battery
The second is the tail plug problem (I don't know if the p20 has a tail plug line, if it does, it is probably its problem, because many of the phones I dismantled before are many problems here)
The third is the charger
There are other questions I don't know...