An iPod Classic does not use iOS 3.1.3 (as noted in your tags) or any other iOS.
If the display says "please wait, low battery" - have you charged it up?
Why do you want to Restore your iPod, whichever model it actually is?
To Restore and iPod, connect it to iTunes, look on the iPod's Summary pane and select Restore. Note that Restore will delete everything from your iPod.
iPods can be Reset, which often sorts out minor problems. How to Reset depends which iPod you have.