I don't know what it is--every iPod nano I've had will stay full for a little while, then drop fairly drastically to half or less, then flirt with the yellow/red like it's almost out, then jump back up to half or more. all three 5th gens do it, and my 4th gen did it too. and yes, ive run the battery all the way down to dead to reset the battery indicator and still they are always wonky. also fwiw if i set the ipod down using apples testing conditions playing music continuously, ill get the advertised battery life if not more so the batteries are good. just really really wonky indicators anyone else?