Surprising?!? Was it a no-maintenance battery? Any paint damage?
http://en.wikipedia.org/wiki/Battery_power#Battery_explosion
Haha, yes, very surprising. Park the car, get cash, turn the key, *BOOM*. Some guys by my car thought a tire popped or something.
No paint damage, that I saw. I'll have to check it out today. The acid got onto some tubes and stuff, but it didn't seem to do any damage at all, really. The car is driving fine, too, so that's good.
And I don't know what you mean by "no maintenance battery". We've never had any problems with it. Never had to charge it or anything.
'Older' batteries had caps you could pry off and top up, most new ones are sealed and the build up of gases seems less likely. (But i guess plausible)