Ya ur battery is done. The same thing happened to me when i washed it, it lost its charge. You can ether take it in to get it done professionally which costs about $80 or you can do it yourself for much cheaper. Here is a link showing you how to replace it.
http://www.everymac.com/systems/apple/ipod/ipod-troubleshooting-repair-faq/ipod-touch-how-to-replace-battery-instructions.html