Dougs rule of thumb on batteries: Get the biggest thing that will fit in a given space. Size=capacity. However, it also equals weight, so there is a balancing act of "reasomable" in the calculation to
consider. It is entirely possible to get a battery or batteries that fit in a space that cannot hold the weight load. Be certain that your floor is strong enough to handle the weight, or add a steel plate under them to spread the load on the wood subfloor.

Doug