Originally Posted by Stefrobrts
So, the question in my mind is, what makes your battery explode like a bomb?!!
Batteries venting hydrogen might cause an explosion in the battery box, but normally won't cause the battery itself to explode. For that to happen, there has to be ignition INSIDE the battery.
My best guess is that the missing cover that you couldn't find was already
missing from the battery, not as a result of the explosion. Then when the spark ignited the hydrogen inside the battery box, the flame back-flashed into the battery through the open fill ports. As the fire tried to expand inside the battery, it expanded faster than the flame could come out the fill ports, and BOOM! That's what an explosion is, a very fast fire that has nowhere to go fast enough to get out of its own way.
Lesson to take away from this (even if it is speculative on my part) never charge your batteries (or use them, for that matter) with the fill covers off.