Today while texting, I got a warning message that my battery had less than 20% remaining. When I looked at my phone it had only 18% left. This was after only using my fully charged iPhone lightly for less than three hours. I had sent and received about 10 text messages, and listened to maybe 5 songs. The problem is that about 5 minutes later while receiving a call, my battery meter was at 78%. What could the problem be? Why would my battery meter say 18% one minute with a low battery warning, and then 78% just 5 minutes later (with no charging)? What should I do? Is anyone else having this problem?