Why does a battery get really hot if you remove the plastic around it?

Question

After i removed the plastic sheet around the battery it got EXTREMELY hot, i couldn't even hold it.

Answer 1

I think you shorted it out somehow, as it normally should be at room temperature.

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Answer 2

Plastic is a good insulator. Perhaps the battery runs at very high temperatures normally, but the heat is absorbed by the plastic and you don't really notice it.