Bart,

Before you start reinventing the wheel, check at your local camera shop. They may have a belt pack power source already made up that suits your needs. I used to have some at work but that was years (actually could be measured in decades) ago when cameras consumed much more power. It was actually a nice set up with two 6V sealed lead acid batteries in canvas pouches for hanging from your belt & the connector was just a cigarette lighter recepticle.

You could also stop in your friendly neighborhood Batteries+ or Batteries Warehouse. Those guys actually LIKE to work with you on building up special application batteries. A few years ago I took bro's Odoscope (it's a doctor thing) in there & they helped me to swap the old NiCd batteries for Li Ion. It worked like a charm & still works to this day.

Last alternative - steal the batteries from the neighbor kid's electric car. Everyone wins ('cept the kid). You get some nice sealed lead acid batteries & the neigborhood cats don't get run over anymore.

Let me know if you need help. I could rig you up something & have it to you before Moab.