There are battery tender caps that keep a reservoir of water so you don't have to check levels as often. If you already have regular batteries to use, check those out.
How about welding some pipe sections on both the frame and battery support, then slide a rod through to support - like a big hinge pin. That way you could pull the pins and lower it with a floor jack.
You could also build a side frame with slots for the whole thing to drop down using a similar concept to this:
You would just have to have one on each side in your case.