Jason-
http://www.corrosion-engineering.com...ng%2007-03.pdf
One of many web references on sulfuric acid resistant
epoxy. I would suggest that you contact a couple of
epoxy makers to ask specifically about their products being suitable for this, apparently some are very resistant and others are not. If you get the right product, acid resistance should be no problem.
I might go a little further though, and when you are done epoxying the space, lay some ordinary felt (from a craft store or fabric store) under/around the batteries and saturate it with baking soda. That way, if any acid spills it is soaked up and neutralized and the inexpensive felt can be changed from time to time as needed. You'll also see where there has been any acid spilling so it is easy to keep an eye on.
Acid spilling out of the batteries at all means they are being overcharged--an expensive way to cut their lives. Or, overfilled and sloshing out, also not good. So once you've gotten the battery space cleaned up again, think about how and why the batteries are being cooked, ideally you should be able to stop the acid from overflowing at all.