It’s a known issue and we’ve fixed it in the latest system update. Please refer to the following instructions to calibrate your battery firmware.
- Update to version 2.20.40.x which is the latest system update for ZenFone 2.
- Shutdown your phone then charge it using an ASUS charger and its ASUS USB cable for at least 8 hours.
- Restart your phone and try again to see if there’s any improvement.