Thanks for the responce guys. I'm gonna bookmark this thread and try and get some of the math down. I'll most like just keep my battery and run it. Truth be told; 2 hrs covers the overwhelming majority of my night time riding anyway. And besides, I don't want to part with it... especially if it's just gonna check out fine.
I'm building another light. One with a Sylvania Tru-Aim MR16 10 degree spot. From what I've heard 'round here, it should really burn a hole in the night compared to the MR11 30 degree flood. And if the MR16 reflectors are really that much brighter, perhaps I'll pick up 10 and 15 watt bulbs to see if they are a reasonable alternative to extend run times when needed.
DanO