Followup - for example I now am playing mp3s on mine for 3 hours/day and that only burns 10% of the battery, because I installed 'magic button' (
http://www.trancreative.com/mb.aspx) which has a nice 'turn off screen' gesture, so I fire up the music and then turn off the screen - still can navigate just fine with the joystick and no wasted power.