This problem is not specific to lithium and/or faulty batteries. Many of these (increasingly common) high-power torches have sealed lead-acid batteries, often just 6 volt powering a 100w bulb so it is drawing nearly 20 amps - as a consequence they get VERY hot and are only designed for very short periods of use. What makes it worse is that the switches are often dangerously exposed and of a very simple and easy to operate lever type. They have their uses but are most definitely not toys, and as has been said, have no place on an aircraft.