Highly recommend just making an appointment at your nearest apple store and getting the battery tested. I had this problem a few months ago. At around 20% capac

Highly recommend just making an appointment at your nearest apple store and getting the battery tested. I had this problem a few months ago. At around 20% capacity my iPhone 5 would shut down. I brought it to the apple store and they said the battery had degraded. They also noticed the camera lens had a speck of dust in it, do they replaced my iPhone for free. Had it not been for the speck of dust, they would have replaced just the battery (at least according to the guy who helped me at the store). (Edited for grammar.)