Ipod battery drains without use. Is this normal?

I've had an Ipod touch since april of 09. I charged my Ipod last sunday (June 26th) and listened to 4 songs. Then 4 songs again on monday. Then last night I used my Ipod for the first time since monday. When I turned on my Ipod touch from sleep mode I looked at the battery and it was full. I then used the Ipod as a flashlight to look for something that I had lost for about a minute and then I noticed that the battery was down by 10 %. I wasn't listening to any music, no apps were running and the wifi was turned off. Does this happen to anybody else's Ipod? Do Ipod batteries drain a bit if you don't use it for 3-4 days or does this mean that I have to replace the battery.