I've owned a few flashlights that use 18650 cells. There was only one that I really loved, but it died prematurely. It was the Fenix PD32. The switch in the end cap died, and I'm not willing to pay the replacement price for it. If you're luckier than I am, you might consider this one.

The trouble with shopping for these flashlights is that there are SO MANY to choose from and not a lot of information about most of them. Most descriptions say they're REALLY BRIGHT but that is compared with expectations, not quantitative. A lot of them are super bright but the beams are too narrow. I walk my dog at night on an unlit road in the country, and my eyes tend to look where I point the flashlight, even when I make an effort to look into the dim portion of the beam. So see if you can see beam patterns, and try to get a light with many intensity choices. You might find that one of the lowest settings is best. I think the designers optimize for brightness rather than battery life. That's too bad, because there's a lot of energy in those cells. Most of the lights I've used only give a couple of hours of use, and they're far brighter than I need, even on the low setting.

There is an entire forum to flashlights. If you think people go nuts here, take a look at candlepower.