There was a recent report on a diving forum of a dive light that nearly caused a fire on an airplane. IIRC, the dive flashlight was sealed, but had a safety switch to keep the battery isolated when it wasn't needed. The diver, on his way home, checked his baggage. The TSA baggage people took the light out, turned it on (apparently to make sure it wasn't a bomb) and then didn't reset the safety switch. The battery, no longer isolated, caught fire. A lithium battery, I believe. This is a known problem with lithium batteries, and the batteries don't have to be counterfeit for this to happen, as far as I know.