The SFE store says 12V http://www.sparkfun.com/products/9218
The schematic says 16V http://www.sparkfun.com/datasheets/DevT … 28-v11.pdf
The MIC5205 datasheet says 20V, but the note on the schematic could be due to capacitor ratings or something. I’d think it’d be ok on a 12V lead-acid battery. I suppose an over-achieving charging system could drive it up to more than 16V, but that’s a risk I’d probably take.