how long Will a fully charged iPod stay charged if you don't use it?

As always with questions like this there is no exact answer. It depends on the type of ipod and the state of the battery (meaning how new is it). Anyway I can only give you an example. I have a several year old ipod touch that I rarely use now as someone gave me an iphone. I leave it in a drawer and turn it on about once a month or so. It always has a little juice left.