This is a controlled short that shows what can happen when an 18650 shorts out. I'm not suggesting this WILL happen, just illustrating that these batteries pack a lot of power, and you want to take precautions to insure something like this doesn't happen. The first and most important step is to be certain your battery cells are legit (i.e., OEM with quality control) and that you use and charge correctly. Not trying to scare anyone. It's just important to know what can happen with faulty batteries and/or incorrect usage. Click to play YouTube Video Edit: Hopefully I am not breaking a rule by specifically talking about battery safety here. Would that fall into the "no discussion of internal elements"?