Hey Joe. The acid had seeped into one spot on the shelf. I first cleaned all the paint away from the entire shelf. The acid actually ate a small hole through the metal. I cut a small piece of metal out and had an expert welder TIG in a patch, ground it back and repainted. There, unfortunately, is no quick fix for a rust-through. If the rust (or corrosion) is only surface, or even deep surface, you can get away with grinding away all the bad metal and, if no penetration, just place a body filler then repaint. Since the rubber pad absorbs all the weight of the battery, you probably won't score the filler. I actually painted the entire area that holds the battery with a PPG two-part body-coloured epoxy paint. The colour match is close and it is a lot tougher than basecoat/clearcoat paint. The battery shelf in these cars is one of their many weak spots and I strongly recommend removing the battery, even after every run. Takes 2 minutes to re-install. I have a shelf that holds the battery up off the floor and out of the way. Good luck.
Bill