i use two numax batteries in my seat box..i leveled up the bottom of the bat box first so they both sit next to each other,the only thing i found with the numax bats i have is there was no handles on them so taking them in and out while we were wiring the split charge up was difficult.we overcome this by using very thick cable ties wrapped around the batteries in a cross pattern so you can lift them in and out easier.simple but works