Also bear in mind that this massive battery was naked in his pocket, which you should never do.
Although protections against shorting the terminals are a standard feature nowadays the very thin layer of skin around the cell won't hold up very well to the harsh environment of a jeans pocket.
One bump into a table corner at the wrong angle is enough to cause a puncture or force a short.
Look closely at your battery before putting it in your pocket. The only separation between dangerous chemicals and your flesh is a very thin plastic label and a thin piece of foil. These batteries were meant to be protected by a sturdy phone chassis and have no hard plastic casing on the back or front.
When carying a spare in a pocket, store it in a small box like a cassette case.
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