Hi
Due to the iPods age it is most likely a bad battery
Battery’s degrade with age even if they are left sitting unused,heat can also affect a battery’s life span
Heres a guide showing you how to replace your battery
[guide|4185|new_window=true]
It is a soldering job just so you will need a soldering iron ,solder and flux to do it
Hopefully this helps
Any questions please ask
Thanks:-)