As reported by engadget,
The Consumer Product Safety Commission is warning customers against purchasing loose lithium-ion battery cells that can be used for vapes, flashlights and other small devices. In particular, the CPSC has issued a warning for 18650 cells, which are slightly larger than AA batteries and are typically manufactured as part of large battery packs. They’ve been popping up on e-commerce websites, though, separated, rewrapped and sold individually. CPSC says using the repacked cells could result in “fires, explosions, serious injuries and even death.”
According to the CPSC’s warning, ,the problem with repacked 18650 cells sold online is that they may have exposed metal positive and negative terminals. When they come in contact with metal objects, such as keys or loose change in the pocket, they could short-circuit and overheat. That could then cause the cells to spew out burning materials.