Time to confess. So, some of my e-cigarette batteries are getting a bit long in the tooth, and one recently packed up all together. I wonder what's inside that metal tube?? Pop it in the vice, prize the top off, there's a small circuit board, and possibly a sharp edge or was that something hot? Whatever, let's force the battery out of the metal tube, there's that hot feeling again....Finally it's out, looks more like a capacitor to me, two thin metal foils with some film/liquid between them. Blimey that's getting hot now, best throw it on the garage floor. Just as well, bl##dy thing went off like a firework, flames jetting out of both ends of the cylindrical battery
Slightly burnt finger but otherwise unscathed, what a numpty, I guess it was the thermal runaway your hear of with mobile phone batteries. Next dodgy one will go in the bin without any outside interference