As h0ughy says, it's good advice to go with a deep cycle. I have an 110 amp/hour unit that I use to power the G11 mount, 8 heaters, SBIG camera and 2 small laptops, and this lasts me for a very long (into the morning) session, and maybe even two evenings until 2:00am or so. A charge using a 10 amp charger refreshes it in one day. Deep cycle batteries must not be run flat - just like a cranking battery must not either. The difference between the two types is that deep cycle batteries are designed to be taken down to the threshold many times wheras cranking (car) batteries are not. They need to be constantly charged and are only designed to provide high level of current (400 amps or more) for very short periods.
Don't use you cars' battery unless you like walking home.
