My Ipod Nano 5th Generation battery display goes down immidiately after I touch the wheel.

Hello,

My Ipod Nano 5th Generation battery display (the green bar) goes down immidiately after I touch the touch wheel. If I leave it after that, the bar fills itself again. This doesnt affect my usage of the iPod, (I can still use the machine for 5 hours+), but its kind of annoying. So I'm wondering is my battery display messed up or is this normal?

Thanks in advance.