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.