I use the stock battery that came with my 744T as backup only, and I carry a NiMh battery pack for primary power. My full rig will run a minumum of 7 hours on the NiMh; that's mic system, 744T (recording 4 tracks at 24/192), CRD420, and task lighting (intermittent cellular phone charging as well).
Obviously, this is not a "stealth" rig, but I have yet to run out of power, and my max draw is around 45 watts at 14.4v. This includes power for burning files to DVD and CDR after a show.
I considered Lithium Ion chemistry, because it has amazing power density, and it is extremely inexpensive, but the tendency for the voltage to spike during discharge, and the sensitivity to humidity, as well as the precautions one must take while charging and the cost of good chargers for Li cells made me choose the NiMh.
Soon though, Lithium Ion will be the chemistry of choice, and I look forward to not carrying the extra weight and physical size.
"If humans matured as quickly as technology, we could fix this world." ---- A visionary.