By coincidence, I ordered my first Elzetta last week (Bones), with optional floody lens, and quickly did some runtime graphs. The Bones is designed to also work with an 18650. Although Elzetta claims the output is highly regulated, that's ONLY using CR123 batteries.

Elzetta claims the following:

What they don't say - is that the steady regulation ONLY occurs if you use CR123 batteries. As you can see in the runtime graphs below, if you use an 18650, the regulation slopes down from beginning to end.

Also, the Texas Ace Calibrate Lumens Tube measured 555 lumens, not 650. And, if using the optional floody lens, it dropped down to 340 lumens (a dissapointing 39% drop in output). I may use the DC-Fix diffusion film, which in the past, has only dropped the output of my other lights by about 10-12%.

Relatively good regulation for about an hour using the two supplied Battery Station CR123. I exceeded Elzetta's listed runtime by 3 min.

Orbrtonix protected 10A 18650 (3,500mah)

Samsung INR18650-25R (capacity tested at 2,471mah)