I have testing this thing and found a few things. An oldere microdrive playing a movie in betaplayer will last about 30-40 minutes--ouch!
Playing mp3's on an SD card with the screen off goes down to 20% battery left in about 2 hours, but wait theres more............the thing lasted another almost 3 hours after hitting the 20% point. It last an hour while 2 different battery monitors showed it with only 5% left. There appears to be a bit of a false alarm on the % left. Five hours playing mp3's with the screen off will get me across the country on a flight--not too bad.