Originally Posted by uncle_bob
Hydrogen can accumulate, but it is very tough to do. The battery is mounted in a way that the gas quickly rises out of the cell. You need a very specific combination of air / hydrogen and spark for an explosion. The cells short normally in a "wet" area. The short is from the plating process that is part of charging. Wet is not good if you are trying to create a spark. When a battery does go boom, things fly around. The terminals are not the big deal in this case ....
When I was a young teen I jump started a tractor that had a 6 volt battery with a 12 volt
vehicle like I had done dozens of times before. This time was different though and the battery exploded... it made a hell of a bang, and it blew the caps off the cells, but no other obvious explosion damage....
So yeah, I know it can happen.
My first response to reading the lead post here was that the terminals didn’t “come off” but they burned or melted off. Someone mentioned that they could have been blown off, so I thought about it and concluded the only way that could happen is if the case were ballooned out due to a small explosion.
My main concern at the time was that there might be a short that is still unresolved that might allow the other still functional battery to start a fire.... i have seen that firsthand too.