What to do if your iPhone 4S battery percentage is stuck and won't change?

My iphone battery percentage is stuck at 100% and I don't know what to do. The only time my battery percentage changes is if I turn my phone off and back on and it'll be on the real battery percentage but it'll still be stuck. Can someone help me with this problem?

Try doing a factory reset, hold down the home button and the shut down button at the same time and it will restart your phone and hopefully sort out your battery problem:)