Longest single use time...
Approximately 40 to 50 minutes, I believe, at a motorcycle accident scene. A minivan made a left turn while trying to beat an oncoming motorcycle, resulting in a collision in which the motorcycle collided with the right fender of the van. The motorcyclist was ejected, landed on the windshield and rolled down the hood and landed directly in front of the van. He had internal bleeding and was going into shock. Nasty stuff.
First the police arrived, and then the EMT and fire crew. The response team made a mistake of erecting the light tower BEHIND the van, so it wasn't illuminating the collision and the injured motorcyclist at all. I had my Scorpion V2 with turbo head, with fresh batteries and everything, so I illuminated the area from about 20 meters away for the next 40-50 minutes while they took the the guy away on a stretcher and tried to clean up the mess, which included gasoline leak that they were able to located and neutralize because of the illumination from my light. With illumination from only the light tower, which was at a really, really, really bad angle, they wouldn't have found out about that until after they towed the vehicle away.
I figure that they never moved the tower around because I had my light pointed at the scene the entire time. It turned quite a bit of eyes, too, because I found that people were staring at me at times.