Haha BatteryGate?
Well maybe, maybe not. I've got 4 iDevices, and about every third software update I'll have one device go wonky on the battery. Charge to 100% and unplug. Few hours later the device will drop 5-10% or more while my other iDevices might have moved 1%.
Easy fix.
"Reset All Settings"
The device will keep all user content, songs, pics, media, app data, but all settings will be restored to default and passwords will need to be re-entered.
ONE NOTE OF CAUTION!
After the device reboots, you'll go thru the grey setup screens (language, siri, etc) At the end it will ask you if you want to setup as New or restore from backup. Choose setup as NEW. (don't worry, you only Reset all SETTINGS!)
You'll get dumped out into your familiar home screen, and you should be GTG.
Hope this helps!