[amsat-bb] Portable power source

So I'm trying to move away from my big, dumb, heavy sealed lead acid batteries for portable work, at least when I have to lug the gear very far. Has anyone had any experience with something like these: http://cgi.ebay.com/Portable-12V-li-ion-Rechargeable-Battery-Pack-9800mAh-/230469117735 ? That looks like it's pretty compact, and will run a pair of 817s a good while. Any suggestions for a more domestic source would be appreciated as well.

73, Drew KO4MA