I'd echo soberbrain's questions. What kind of iPod (some of them have had battery "issues") do you have? How long is a standard battery charge? How old is the iPod? I'd suggest trying to charge it up (fully) and then see what happens. You can then time how long the battery actually lasts. It may simply have been left on all night unknowingly; however, if after that, you cannot switch it on/off, or the battery drains precipitately, you may have a more serious battery problem.
Twice, an iPod of mine died (battery issues, with both of them) and, as they were still under warranty, both were replaced without any difficulty (which was one of the reasons I became a switcher). Let us know what happens; good luck with it, cheers.