Flooded lead acid batteries can and will explode. How do I know? Because I've done it. It takes some work (and a momentary lack of intelligence) to do it. Here's what I did.
On my first car, with small block Chevy V8 and and aging battery, I decided to perform a compression test. Since the battery was weak, I put the shop 50 amp boost charger on it as I performed the test so that the battery would not go dead. The battery began to gas. I cranked the starter several times as I checked the compression in the various cylinders. So, the battery was discharging from the compression testing, AND, at the same time, being charged (at 50 amp rate) from the charger. I accidentally clipped the charger cables with my elbow, (spark occurs) and BOOM! The caps blew off the battery, the lid on the battery split in several places, and battery acid went flying everywhere, including in my eyes and on my clothes. So, yes, IT CAN BE DONE!
You really have to work at it though. Even with trickle charging, IF THERE IS NO ADEQUATE VENTILATION AND SUFFICIENT TIME, it is possible to concentrate hydrogen/oxygen sufficiently so that if a spark presents itself, . . . . . BOOM! In a confined space, expect the worst. Unlike gasoline, hydrogen is explosive at very low concentrations. (lean mixtures)
Chum lee
