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

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.