Phone battery
Rule of thumb- Don’t puncture anything with “Battery” in the name, although I wonder if this is actually a phone battery or not.
This was an actual known issue with some phone batteries, namely lithium based ones, at one point, that they get really hot and can start fires or even explode. It takes quite a bit of force to do it, or a lot of voltage, or just a matter of getting too hot from, say, ending up under a pillow or bedding, or just having a cheap replacement battery that gets over charged.
KA-BOOOM!!!
