The best lights to keep in a car are not much different than the best lights to keep in your home. They need to be capable of a wide variety of tasks in, under or away from the vehicle. The wife’s car has 2 18650 powered lights. 1 is a headlight. They both go from moonlight to 1000 lumens and have similar UIs. The batteries are interchangeable. The tail caps are loosened a quarter-turn and she knows that. She never uses them. I try to check them every 6 months or so. I’ve got a few lights in my vehicle, all but 1 use a 18650.