iPod Touch 5G Won't Stay Charged?

I bought my iPod Touch 5G for $400 in December of 2012, and it worked amazingly for awhile. Unfortunately, I started noticing the battery is struggling to remain fully charged or charged at all. It dies within hours, an having paid $400, you can see why that's a problem. I have tried restarting, resetting, and rebooting. It still holds the same problem. When I charge it, I can't get the full charged symbol in the battery icon. I have tried closing all apps and the email thing, all of that. I have heard a lot of people say the iOS is the reason (6.1.3). I hope this is the problem. What should I do? Should I buy a new one or risk waiting for the new iOS?