You are right zespectre, they can be extremely dangerous. Our flashlights do not have a failsafe, and they have already become powerful enough to deserve one due to the amount of energy they store in cells. Because regardless of who is to blame, when a lithium based cell wrapped in a metal sheet explodes, it is always very dangerous.
I saw what an ordinary, common 9v battery does to human hands when it explodes. The poor guy lost some fingers and both hands were full of shards, splinters, chips and other fragments from the cell, leaving him with a lasting disability. Fortunately he can use both hands now, but they are not what they used to be.
I admit it was not a lithium cell, but they can explode as well. And the consequences are the same from a lithium or nickel-cadmium or alkaline or nickel-metalhydride or any other cell. They all can blow up.
Honestly speaking, in that particular case it was entirely his own fault, because he was charging a non-rechargeable 9v cell while holding it… Stupid beyond measure… I don’t have words for that… But we all do stupid stuff from time to time and call it “hobby” or “modding” or “direct drive” or “testing” etc.
I do not want to say they should be banned, but these things should be approached with respect and common sense, nothing more. And not everyone is mature or reasonable enough to use them.