Outer Limits 4x4 Board

Does anyone know if you can fit a 2nd battery (sealed, optima type) under the passenger seat of a RHD (Driver seat of a LHD I suppose) of a RRC?
I have no room under the bonet due to other mods.
If it will fit, what are the possible problems as there are definately some good advantages.

If it will fit,...
you could fit an Optima on its side, have a look at their web site to get the dimensions. Remember that there are a couple of seat brackets that slide back and forth as you move the seat... probably need to make a cardboard box the battery size to confirm no size problem.
Then again you could cut a battery box into the floor, give you plenty of room.