Wow, that was exciting…
My Samsung S9 battery bloated up popping the back cover open. I bought a replacement and was in the process of changing it when the old (bloated one) shorted somewhere inside in the bottom corner of the battery. It started by glowing in one small point then the whole thing started sizzling making lots of smoke. I tried to take it outside but made only a few steps before the whole thing got hot and scary to hold in hands, and I had to drop the phone. The battery remains popped out and started glowing red (I’m not exaggerating) then caught fire. Fortunately that main burning piece of the battery landed on the concrete part of the floor. The pieces that landed on the carpet were so hot that they melted it. Those were not thick big pieces that can absorb a lot of heat, pretty much just a copper foil (I guess with a bit of still reacting lithium).

The tip of the day: BE VERY CAREFUL PRYING OUT LI-ION BATTERIES, ESPECIALLY AVOID THE CORNERS.

Surprisingly, the phone still works, just the speaker board needs replacement…
And as I recently noticed there is now a yellow tint in a few places where LCD was damaged by the heat.