....The security guy in Rome took the batteries out of my 4x18650 light and put them in my box, but not the two smaller lights I had with me. That's the closest thing to a problem I've ever had.
Yes,
you are more likely to have security screening problems if anything resembles a possible weapon.
Federal regulations prohibit the exportation of tactical flashlights; large lights raise suspicion, especially if heavy because of batteries they contain.
It is a good idea to carry printed copies of the latest I.A.T.A. guidelines, remove crenelated bezels, and even take the lights apart if possible.
FWIW, more than once I have had to completely empty and display the contents of my carry on with up to 30 lithium ions of various sizes, two large Anker power banks, chargers and up to ten flashlights, a couple of them Soup can lights.
The first time it happened, the inspector remarked, "Oh, you're a photographer?"
The following times, it was the explanation I offered.
There was never any instance when they made things difficult.
If you are carrying anything onto a plane you deem capable of raising suspicion, I have a suggestion:
Pretend you are Gomer Pyle or Forrest Gump, you be cool, it makes all the difference.