[jsmay311]

I don't know the capacity in Ah of the 12V battery, but assuming it is 250 Ah or greater you would only use about 10% or less for 30W / 10 hours.

250 Ah on a 12V battery would be 3 kWh.

I had a surprisingly difficult time finding any specs for a Gen 2 Volt-compatible 12V battery, but this Gen 1-compatible battery one at Autozone specifies 60 Ah. http://www.autozone.com/ignition-tu...ery/duralast-platinum-battery/338292_537162_0

Sounds like a bad idea to me.