Open the Phone app and dial `*#*#4636#*#*` if supported
Go to Settings > Battery
Check Battery usage in Settings
Use the device’s built-in diagnostics app
Open Samsung Members > Diagnostics > Battery
Open Xiaomi Security app > Battery > Diagnostics
Open OnePlus Diagnostics or Device Care
Open Motorola Help or Device Help > Diagnostics
Open Google Pixel Settings > Battery > Battery diagnostics
Install a trusted battery health app from the Play Store
Check battery cycle count in supported device diagnostics
Look for fast draining, overheating, or sudden shutdowns
Compare current full charge duration with original performance
Check battery status in recovery or service menu if available