I used 24 6V golf cart batteries from Les Schwab to power my rig. 6V seems to be the choice for maximum range (don't ask me why). Then the lights and radio and blinker run off a 12V auxiliary battery that is a deep cycle type battery. This is important since it will be used and only charged when plugged in, not like a car battery which is continuously charged by the alternator.
The 6V units are flooded which means you have to fill them with water every month or so. I haven't done this yet, maybe I'll post about it when it comes time.
I have 10 batteries in a box behind the drivers seat which has a 110V computer box fan attached to vent the explosive battery gasses during the charging process. This is a box I made out of wood and non corrosive plastic sheeting material. it is bolted to the floor and reinforced with some angle iron inside and a steel strap around the whole box.
The auxiliary battery is where the original battery went, and 10 more are on a wooden platform above the motor, and the last 4 are in the compartment that the gas tank used to be in.
The plugs for the battery charging come out through my old gas door. I just had to.