my ipod only works when it is plugged into its charger. is this just a battery replacement issue?

Yes. You can have Apple replace it, a third party repair company ( a little less cost), or you can even swap it out yourself if you feel up to it.

B-rock

I'm having the same problem and it's a new iPod (only purchased 4 monhts ago). I've only just got around to using it and it only works when either plugged in and being synced in iTunes, or when it's plugged into a charger. As soon as you unplug from a power source, it goes black and won't turn back on. It doesnt even appear to power down, it just goes black.