When I flew large electric r/c helicopters, I used to run my high-current battery chargers from a deep cylce marine battery when in the field. The chargers would output 24A for 6 minutes no problem.
I noticed voltage drop after a few charges in the field, which lengthened charge time. For this reason I decided against using a deep-cycle for the Nomad II. It would be more convenient to not have to open the hood that's for sure, but I'll stick with what I'm doing for now.