Hi
I think your battery is degraded as iv seen iPods do this before and usually charging it through a Mac or pc works
also I have found that 9/10 a firewire charger will work as they output more than the usb ones
apart from that it might be time for a new battery but I would try a firewire charger first
if you can find a firewire charger for a good enough price I recommend looking locally for people selling old iPods that come with the charger
Hopefully this helps
Any questions please ask
Thanks:-)