Are you using the stock incandescent bulbs or is this an HID conversion? For my HID conversion, I'm using 2 Prismatic style 4S/5000 Lithium Poly's. For incan bulbs, you could use 2 ea. 3S/5000 packs in parallel. As with the SLA, you will not be driving the bulb at max power but you will get about the same performance with more run time 7AH vrs 10AH. Two packs will fit in the same space.