So I bought a used 64GB (storage is the killer app for me) iPhone 5 off ebay (first mistake?), and everything seemed pretty normal. Then I started noticing something weird about the battery behavior. It seems to charge normally and drain normally, that is until it gets down to 20%. The moment I get the "Low Battery" pop-up I've got 10min max before the phone is dead. Then I noticed another thing. When I plug it in to charge it, and it finally comes back to life (nothing irregular there either), it's back at 20/21% batter life! Now one day, I hit the 20% threshold and about 5min into my final stretch I decided to turn off wifi. The phone stayed charged with intermittent use for a few more hours as it normally would. Has anyone run into this or a similar issue? Was there a solution? Could it be a cheap Chinese battery? I've replaced the battery in a couple iPhones and never seen this behavior, so I'm a little mystified.