Sometimes you Android may show you the wrong battery information.You can fix this problem by calibrating your Android battery..Calibration correct your battery stas and allow Android to show correct battery info..You can do it easily using calibration app.Battery calibration apps are availabe in Google Play store and you need root acces to use calibration apps.If you do not have root access, you need to do it using manual method.
Discharge the device completely > Turn on and let it turn off itself > charge the device to 100 % without turn on >Unplug > Turn on
if it is not 100 %, plug the charger without turning off it
When 100% unplug and restart
If the battery still below 100%, repeat the cycle
unplug the device and let it discharge to 0% and turn off
Full charge it
Now, you have calibrated your battery and device will not turn off before reaching to its minimum level. if you want to use calibration App, learn android rooting first here, https://odindownload.com/root-android/