One of the first things I did when I got my maglite 6D, (which I love,) is to put a ring of duct tape around the batteries. Now the battery doesn't go "clunk" every time I change its orientation! It feels a lot better!
It's an old trick. A lot of people use post-it notes and write their name on it just in case the light "takes a walk."
Probably not a big deal in most flashlights but be aware that duct tape will conduct electricity. Really not a good thing to find out after you've fixed the wiring in the car.