My Ipod touch turns off and restarts when charging? Please Help!

My Ipod touch turns off after 4 minutes of charging and starts up again to do the same thing. it has a short battery life of a day without being used much. The battery icon( the big green one) starts going up to fully charged when dissconnected but when connected it decreases until it restarts again. why is this I think it is a firmware fault as it seems to stay on when in recovery mode.
Thanks!