I have mentioned this before in the subject of battery explosions. Back in the 60’s I worked in electroplating, mostly pioneering plating on plastics. We had an acid copper bath in our shop to build up thicknesses after electroless plating and it didn’t seem to be working. It had a variable voltage power supply and a 6V lead acid battery for smoothing the repple from the rectifier. The battery had three cells of about 1 gallon capacity each, so quite big. Ray said “lets check the battery and I handed hin a nickel plated steel bar from a drying cabinet, about 5/16” diameter and he squatted down above the battery and I leaned over him to get a good view. He shorted out the battery and one cell exploded and left nothing but an empty gallon container. Everything had gone upward and neither of us was touched by some sort of miracle. The MD soon arrived to see what had happened and our excuse was that our firm had been developing “catylators” which screwed in replacing the filler caps. They were fitted to every battery in the place. They contained a tiny ammount of palladium chloride which recombined the hydrogen and oxygen gasses into water rendering topping up unneccessary. Our rather pathetic excuse got us no more than a stern telling off. The replacement battery was 280AH and not quite as big as the old one.
I have treated all lead acid batteries with respect ever since.