A coach battery exploded on my RV last year. I found a loose cable going to the battery which probably sparked, igniting hydrogen gas out-gassing from the battery. BTW the loose cable connection was within the copper connector that is used in attaching the cable to the battery.
I also once had a battery explode when I jumped a car at the car wash. The explosion blew battery acid all over the front of me. Fortunately, I was able to hose off the acid before I got any burns. It did destroy the cotton t-shirt I was wearing. A hard way to learn to never connect the ground cable to the battery but rather to the engine block or car frame.
Steve