Well every thing's regulated so the power source can be anything from 10V to 30V. I can actually get away with less voltage but then i can only run 1 headlight as the 3404 is a buck regulator and has some drop out associated with it.

I can use SLA's and they're my good old backup. I also utilize used batteries from work. In our pipeline pigs we use electrochem lithium batteries (not lithium ion). These batteries come in the standard battery packages, AA, C, D and Double D, but each cell has a voltage output of 3.9V and the AH ranges from 5 for the C to 30 for the DD. As per company policy, a new set of batteries is used for each run, which means there's allot of batteries with allot of life left in em. oh, and off the top of my head, each 'C' cell is costs about $80, you wouldn't want to use these things if they weren't free