Hi,
Try starting the phone in safe mode and check if the problem is still there or not
''To get into safe mode'':
Hold the power button until the options come up (Power off, Reboot, Airplane mode etc...)
Hold the Power off option until the safe mode dialog pops up.
Confirm that you want to reboot into Safe mode.
''If for whatever reason this does not work try the following'':
Power off your phone, then power it back on.
As the Mi logo comes up, hold the volume down button until you boot into Safe mode.
If it works OK in safe mode then a ''downloaded'' app is the problem.
The trick is to find out which one.
You’ll need to uninstall each ''downloaded app'', one by one and test the phone in normal mode to see if it works OK or not. When it does work OK then the last downloaded app that was uninstalled was the culprit. Try starting with ''downloaded'' apps that were installed or updated about the time the problem first started.
If it is still no good when in safe mode, does it do this with the charger connected and switched on?
If not then try replacing the battery and check if that resolves the problem.
Here’s a link to the ifixit [guide|125727] guide, which may help.
Replacement batteries are available online. Just search for ''BM3L battery'' to get results for suppliers