any battery backup that has to tether to the device defeats its functionality..just like these bulky cases ive been seeing....would be nice to have a battery backup in your bag for emergencies (I guess if your stuck in the woods for a week and only have your ipad to keep you sane) but the weight of an 80 hour battery might make it not worth it.
My need involves having a battery backup during power outages so IpadOne's solution could be perfect for my needs.
One of the reviews posted today cited a >12.5 hour run time with wifi on, screen brightness at full, all power saving features off playing video continually. If I had a power outage that lasts longer than that, I'd think I'd be taking it to my local coffee shop and plugging in there while I re-caffinated myself.