My 4s sometimes shuts itself off, without the battery being low. It usually happens when I'm taking a short video or photos. The phone shuts off and the charge battery sign appears, but after a minute or two, I can turn the phone back on and it says 20% or even higher sometimes.....It makes no sense. Today when I was taking a video, it said 1% left, so I quickly connected the charger before it shut off, and it automatically changed to 63% !!!! What's going on with it?