It’s rare, but every once in a while you hear about somebody who had a battery explode or catch fire.
The most common result of a catastrophic battery failure is that it vents gas, or maybe splatters a little bit of the electrolyte around (that’s acid, not what plants crave).
As a side note, there are actual battery spill cleanup kits that you can buy that have everything in them you would need to properly clean up a catastrophic battery failure. The one in the picture above can be found here and retails for about $170. I’m not saying you need one of these, just a heads up.
First, if the battery is just hot and hasn’t actually failed yet, get it out of the house, and on or in something not flammable. I keep a large ceramic pot full of sand (stolen from Pismo Beach in an act of drunken idiocy no less) outside of my house for just this purpose (it used to be my ashtray when I smoked, but it’s always been ready to do double duty as a ‘battery in meltdown’ receptacle), with a small metal pail next to it to act as a cover. A small metal trashcan from Home Despot filled with sand would work just fine.
There are a number of things that the battery can do once it reaches volatile heat levels or begins a thermal reaction. Stay away from it until it is ambient temperature (one of those laser non contact thermometers is really handy for knowing when the reaction is done).
The most common is a gas vent. The battery case ruptures and vents noxious gas. If it happens in the house, open the windows and go outside to call 911. You don’t want to be breathing this stuff.
IMR batteries are most likely to fail in this way, which is why they are generally considered to be the safest for use in APVs.
How you react to a failed battery kinda depends on what kind of battery it is, and what it does.
Lithium will burn in a normal atmosphere and reacts explosively with water to form hydrogen. The presence of minute amounts of water may ignite the material and the hydrogen gas. Lithium fires can also throw off highly reactive molten lithium metal particles. Cells adjacent to any burning material could overheat causing a violent explosion.
If you are using a Lithium based cell, and it starts getting hot, smoking, or ruptures, do not throw water on it, or throw it in water.
If you took high school chemistry you’ll probably remember acids and bases, and that they can neutralize each other. If a battery ruptures, leaks or pops, you should pour baking soda or soda ash (if you happen to have a swimming pool you may have some soda ash) on it to neutralize the acids in the battery.
Kitty litter absorbs this stuff pretty well too.
If you have a fire, there are two components that must be handled; the battery material (or the primary), and incidentals (plastic from the wrapper or charger, wood from cabinets, etc., or the secondary).
The primary should be handled by a Class D fire extinguisher ideally. Who the hell has a Class D extinguisher? You can buy them at places like Jorgensen’s, but unless you have a stockpile of the things it’s probably not necessary. Tossing a package of baking soda on it should suffice. If it does not, get out of the structure and call 911.
Secondaries can be handled with a standard Class C fire extinguisher. Most people have these in their homes (or at least the ABC variety. If you don’t you should stop reading this and go buy one. Seriously. Fire is no joke, and a small extinguisher could save you worlds of problems). I have a Class C in my bathroom (where I do all my battery charging because everything in there is tile), and an ABC in my kitchen. I also keep a box of baking soda in both places.
Once you have everything contained, call poison control and find out how to properly dispose of the waste. Don’t just toss this stuff in the garbage. It can be dangerous, it’s illegal, and it’s just kind of a dick move.
I’m not a hazardous waste expert. I am not offering risk management advice. I’m just sharing the information I have with you. If your house burns down because you listened to me, don’t try to sue me (at best you’d only get some used Metallica CDs anyway).