How to reduce battery drains problem after updating MIUI :
Do a factory reset after updates.
Go to setting - Developer options - Memory optimization - set low (default set is middle)
Go to setting - Developer options - Background proses limit - set No background proses
(default set is standard limit)
Go to setting - Simcard&Mobile network - set data plan - turn off Allow background data
Go to setting - Battery - Power - Turn on battery saver.
Go to setting - Battery - Manage app battery usage - Choose apps - all apps either
installed and system apps set restricts background activity.
- Tweak doze setting - install Greenify apps from Play Store - go to its setting - enable
Aggressive Doze and enable Doze on the go (if your phone not rooted also can but need
to follows its guide. You must connected your phone with pc and go to command promt
or cmd in order to enable Doze on the go function on your phone)