Hello there jiyaspatel,
It sounds like you are experiencing less than expected battery life and the batter seems to take longer than it should to charge. I would start by troubleshooting the software on the iPad mini by quitting all the running apps:
Force an app to close in iOS
1. Press the Home button two times quickly. You'll see small previews of your recently used apps.
2. Swipe left to find the app you want to close.
3. Swipe up on the app's preview to close it.
When you have done that force restart the device and test both backups again:
iOS: Turning off and on (restarting) and resetting
If the issue persists, backup your device to iTunes, then restore it as new and verify that it works.
How to erase your iOS device and then set it up as a new device or restore it from backups
If it does, then restore your backup to either verify it still works and the software just needed reinstalled, or isolate the issue to the backup file itself.
If none of that works then you will need to seek service for your iPad:
iPad Battery and Power - Apple Support
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