Dangerous?

Many years ago, part of my training was there was a risk of explosion around batteries. Years later, got to the job, and loader would not start. Opened batt box, and found a loose cable. At the same time the owner put his son in cab so boy could crank while dad sprayed. I saw what was happening, bent to reach the master switch. Because I was reaching for master, the blast missed me, but I was not fast enough to get out of the acid rain. Not sure I want one in the bedroom.
Somebody mentioned old VW. In years past batteries have been accessed from inside the cabin, but I can't think of any that where not sealed from the cabin, and vented to outside.