Many users complain about the battery issue, so some one from reddit make a tutorial about resetting the batter.
Step 1 Let your iDevice completely discharge until it automatically shuts down (0% battery left).
Step 2 Leave it off for at least 5 hours (best overnight) without trying to turn it on.
Step 3 Charge your iDevice to 100% while leaving it idle. Only use official Apple cables.
Step 4 Leave your iDevice charging at least 2 more hours after it reaches 100%, to make sure that the battery is charged at its maximum capacity.
Step 5 Your battery should now be reset. If your problem persists, try restoring your iDevice with 3uTools before going to an Apple Store.
NOTICE: if you have either a beta version of iOS or a jailbroken device, it’s entirely possible that your battery is suffering from it. Try switching to a stable iOS version without jailbreaking it.
By the way, you can check your battery situation on 3uTools.