Batts: LIR123 vs 18650 in Cree application

[voxluna]

Having used Streamlight tacticals LONG ago (1990 on), I'm not new to rechargeable lights. But I'm relatively new to all the modding and interchangeability.

Apologies in advance if I've missed some critical sticky thread. I've been reading through the site for a couple weeks, scoured the Welcome Mat (even found a typo!) and am taking in a lot of info. That said...

I am trying to define the advantages of using one 3.7v 18650 battery instead of two 3.7v LIR123A's. They are both (roughly) the same form factor. My common sense says, "lower voltage, lower (light) output". And comparing the mAh seems to say they are close in lifespan. Is it a tradeoff of output vs runtime in this situation?

Then you have the LiFePO4 situation, which is supposed to alleiviate lights with the "3-8v" problem. But 3.7 x 2 = 7.4v after settling. What gives?

Last but not least, is there a list showing flashlight parts equivalents to the more expensive, say, Surefire model? For example, this Romisen RC-E4 Cree has a tailcap similar to a 6P. However, my UltraFire WF-502B Xenon has a tailcap that seems nonstandard all around.

Any other advice/tables/threads of interest would be appreciated.

 

[limecc]

Two of the brightest reference Cree lights available - Dereelight DBS V2 and the Raidfire Spear both use the 18650. The Driver circuits are optimised to output to the LED from the lower voltage. 2 x 3.6v's would drive the emitter directly and damage it so output is not really dependent on voltage, rather the light design.

Two batteries hold less energy - ie 2 x 880mA (16340's) = 1760mA where an equivalent branded 18650 holds 2400mA.

I own a Fenix P2D and Raidfire, so I am using both form factors. For me, I enjoy the P2D's small size and am happy to carry a spare battery rather than have a P3D which is a battery length longer and has twice the runtime. For more throw and runtime, I would much sooner purchase a small 18650 light than the P3D - no contest.

Just my opinion..