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