Burning isn’t as likely. But I had my old iPhone 4 or 5S battery swell and destroy itself that way while sitting in temperature controlled storage for a couple

Burning isn’t as likely. But I had my old iPhone 4 or 5S battery swell and destroy itself that way while sitting in temperature controlled storage for a couple years. I won’t be storing such items in combustible containers anymore even though the risk is pretty low and they mostly just swell.