iPod classic battery drains

Was wondering if anyone else had this problem since I haven't seen it posted here? I noticed a couple weeks ago that my 160gb iPod seemed to lose it's battery power when I had it sleeping. Then Friday night I gave it a full charge and listened to it for only 5 hours on Saturday. Put it back to sleep and Sunday morning my battery was dead! What the heck is going on? I noticed when I hold "play" to put it to sleep it takes a second or two less than the older models. Can anyone please help me on this?