I was doing an obsessive/compulsive cleaning out of the trunk today (no, not to get rid of evidence of a crime) and after taking out the spare and associated attachments I got a look at the battery one normally doesn't get, and I also get a bit of an unpleasant surprise. In the left front corner of the battery, right around the vent tube, there was a pile of powdery material (dry) as well as some bare metal and rust where the paint was eaten away (see pic if it attaches).
I can't recall my high school chemistry (or college, for that matter) all that well, but I guess the stuff might be a salt product of an acid reaction. The strange thing is, though, I couldn't find any obvious crack in the battery or sign of seepage from a vent cap, so I don't know what the heck is going on. I do make it a point in the fall and in the spring to keep the cells topped up, but not to overflowing.
Anyway, my point is this will need some body shop attention, it's not an area to risk weakening, and I do suggest that you take a peek yourselves, pull out the spare and disconnect and pull out the battery (remember your radio code!) to see what's going on with your vee-hi-cule.