ipod video dies over night. i have replaced the battery several times, still dies. Any solutions?

Hi everyone, my ipod video plays music for several hours, as it should, without dying. However, it dies in approximately the same amount of time even when it is not playing music and is in sleep mode. I have tried 2 brand new batteries and some old ones that are known NOT to drain on their own, and the problem still persists. Has anyone had this problem and solved it, or will this remain a mystery? Any ideas (other than try a new battery) are welcome.Thanks in advance.