I had a truly frightening experience with TSA once.
I had a NiMH HID light for cave diving that I kept in a Pelican case. In case you're not familiar, the HID lights have large canister batteries. The light doesn't turn on right away when activated - it takes a couple of seconds to illuminate. And the light gets very hot when turned on, and needs water cooling. The light head can be plugged into "dummy" battery slots for storage without risk of activating the light.
I usually hand carry the light with me on the airplane. But on one occasion I placed the HID light and Pelican case in my checked suitcase. I triple checked make sure that the light head was plugged into the "dummy" slots in the battery.
When I returned home, I opened my HID light Pelican case and was HORRIFIED. Inside of the Pelican, was a charred note from TSA that they had opened and inspected the contents of the Pelican case. The light head had been plugged into the battery terminals and the switched was still turned on. The light head was completely melted, and the other contents of the Pelican case were melted and charred.
My belief is that TSA plugged in the battery and turned on the light. When the light did not turn on right away, they figured that the battery was dead and put the light back into the Pelican case.
TSA adamantly refused any responsibility for my destroyed $1,500 light. Of course, insurance only covers $400 of checked luggage.