It's not just LiPos: while the 18650 are (afaik) safer to charge, they have the problem that the entire outer part except the top is the negative pole. Meaning the slightest damage to the wrap can cause it to get exposed: if you put to batteries in series, next to each other, and their negative poles touch, max current flows and produces enough heat to set things on fire and possibly causes explosion. Happens every once in a while in the vaping community for instance.
