In general, I try to avoid in-home explosions when I can. I mean, nobody’s perfect, and, sure, some explosions are going to slip through the cracks, right? Of course they will. Like the explosion that must have happened last night, to a car battery I kept in my basement office/workshop/dork lair.

I didn’t even notice anything had happened until my kid, down in my office with me, noticed what he thought was an oil spill in the workshop section. Not recalling spilling any oil, I went over to see if the cats had knocked over something while trying to torture one of the voles they bring into the house, but that wasn’t the case.

Not only was there a lot of strange, wet black stains, there were also bits of jagged black plastic all over the place. I followed the trail of detrius up to the little cinder block steps to where I was trickle-charging a car battery, which proved to be the source of the explosion.

The explosion must have happened sometime in the night, luckily when no one was around. What I don’t understand is exactly why it happened.

I know car ; usually this happens when a battery is older and being jumped, or used to jump another car, or cranking a reluctant engine, or under some sort of stress. Inside a battery are a grid of lead plates, soaking in sulfuric acid, the reaction between the two generating the electricity.

A byproduct of this reaction is gaseous hydrogen, which is very flammable. Any little spark could cause the hydrogen to combust which is, of course, bad. If your battery is already old and has suffered some internal water loss, the lead plates can become exposed to air in the battery, and if the battery is under high demand, the plates can flex, make contact, arcing and making sparks, which can ignite the hydrogen, and boom, battery explodes.

Dirty terminals can also be a source of sparks, since they cause bad connections and electrical arcs. So can touching cables while jumping the car, or any number of other things.

But I wasn’t doing any of that; the terminals were clean, and the battery was on a trickle-charger, as it has been for a couple of weeks. People leave batteries on trickle chargers for months—that’s what they’re for: to keep a battery charged up enough to keep from losing too much voltage.

So, I don’t get it—the battery wasn’t new, but it wasn’t that old, it had clean terminals, no load placed on it, and just a trickle-charger drooling electrons into it. So why did it explode?

I’m not sure, but I’ll be looking into it. What I do want to pass along right now, though, is a reminder that sometimes unexpected things can happen. I was lucky in that the battery wasn’t in a car or near anything valuable.

But if you have a battery in a car or otherwise you’re trickle-charging, maybe take a moment just to check on it—are the battery’s vents clear, if available, are the terminals clean, are there any sources of sparks around?

Be careful, pals! These batteries are not to be trusted!