To calibrate an Android device battery without root access
Discharge your phone fully until it turns itself off.
Turn it on again and let it turn itself off.
Plug your phone into a charger and, without turning it on, let it charge until the on-screen or LED indicator says 100 percent. Unplug your charger. This site offers other solutions that might be helpful
https://www.androidpit.com/how-to-calibrate-the-battery-on-your-android-device
Hope this helps