I’ve got to agree with you’ll on this one 18650’s are a little small for 3500 lumens. 21700’s are the future. Still companies cling to the 25.4mm body tube for light mounts, 30mm mounts are also available. For 4.6mm’s you get a better battery for 3500 lumens, a much longer run time and a little more meat in the tube. With some companies producing several similar lights it would be nice for and after market upgrade in 21700 size for those 99% that never mount a light on a firearm. I’ve got a few Klarus lights and I would love to upgrade/improve them into the 21700 format.