Hi I recently purchased an iPhone 5 in great condition off eBay. Since I bought it it will die at random percentages. Sometimes it'll be 20, sometimes 5, 7, or 15. I have never gone below 5 so far. I did do a reset via iTunes and reinstalled everything and that didn't do anything. Any ideas what's going on? I asked Dr. Google and the two options I saw were either one I have a faulty battery or it's because of iOS 7.1. I get about 9-12 hrs of battery life a day(spend a good portion of the day without signal so it's searching) even when dying at 15 percent. When it dies I get a 'plug in with red battery sign'. What's going on?