Why should you keep batteries topped up?

[Bbqjoe]

This is why.

This battery sat installed, but was neglected for some time.
The electrolyte had all but gassed off, leaving a small amount in the bottom, and the rest of the battery was full of gasses.

The battery was called upon, and shorted out inside, igniting the gasses.
These are just some of the pieces found.
The explosion was much louder than a 12ga.

 

[Kartorbust]

Well does the sound like you got hurt, outside of ringing ears and dirty shorts from that. Wonder if "maintenance free" batteries could have the same fate?

 

[chancer]

I have seen that happen once before.
It will definitely get your attention!

 

[Bbqjoe]

Fortunately it was in an enclosed environment.

 

[tinamcjittles]

I wanted to figure out what makes them explode and found this.
"The most common reaction byproducts associated with sulfuric acid (H2SO4) are hydrogen and sulfur dioxide. "
Hmm, would you look at that, all the necessary ingredients for a mini-bomb! A fuel (hydrogen) and its friend oxygen in a nice pressurized container!
.
I'm actually happy to have learned this because I try to revive these old batteries a lot and didn't know they could explode!