Your extinguisher will do absolutely nothing. Get rid of it. Soon. Better now.

The extinguisher is not for the battery itself silly, it's for when everything else around it is on fire :)

But if the fire continues after the extinguisher is done… what is covering that scenario?

At least put it in a coffee cup or something like that!

How am I supposed to be able to observe it slowly swell more over time then? I think I might have overstated how big this battery is, or understated how small it is. It's fiiine :)

YES!!

The other thing to do is discharge it, so it has little energy stored to maintain/enlarge a fire

A drone engineer I worked with would immediately put any suspect battery into a barrel of water for several days, then get them disposed of properly.

The risk really seems trivial, probably because of our extensive experience with ordinary alkaline and NiCad batteries with a very benign degradation pattern, but the risk with Li-Ion is no joke.

All your fire extinguishers will do you no good if it goes off while you are out of the house. Also, the fire extinguishers will only suppress the surrounding fire, and do nothing about the core Li-Ion fire itself.

It's trivial until they go, and then it is instant misery. I've done it on purpose just to see how bad it would be and even knowing it will happen it will still surprise you with how sudden, total and hot those things burn. You have < 2 seconds from first signs of ignition to all-out fire with the battery moving all over the place due to outgassing. It's a thing to behold.

Lol, literally none of those will meaningfully reduce or stop the damage if it happens.

Very applicable example for the thread!