dude, virtually no one makes anything packing more than 4 18650s, because nobody wants to pack around such a ginormous flashlight.
Some background. Lumens in terms of power required function in a linear fashion - twice the lumens requires twice the electrical energy. However, from a subjective brightness point of view, lumens scale in a exponential fashion. You need something like 5-8x the lumens to get 2x the subjective brightness. So your Fenix TK76 at 2800 lumens is subjectively only about 4-5x as bright as a 50 lumen light. Incidentally, that’s 2800 lumens in “turbo” mode, which generally means it only outputs that for a few minutes before ramping output down to something close to its “high” mode so that it doesn’t start melting its electronics.*
The confusion you have over the battery capacity comes from the fact that it accepts both Li-ion 18650’s and Li CR123A’s (which are half the length and hence twice as many fit.) Well, sort of. The documentation is legitimately confusing. The glossy brochure says it takes 4x 18650 or 8x CR123A, but the manual says that you can’t use CR123A (presumably because you get double the voltage from them because they are inserted in a series configuration, and if your circuitry isn’t designed for that the magic smoke will be released. However, it apparently will also run with just two of the four battery chambers filled, so you can if necessary run on just 2x 18650, and perhaps in this configuration you can put 4x CR123A in? Not sure, depends on how the battery carrier is configured in terms of the cells being in series vs being in parallel. Anyways, to confuse things even further, on top of that there’s an optional “extended runtime” accessory that doubles the handle length and moves it up to an 8x 18650 capacity. That accessory is actually from the TK75 model, and the TK75 manual says you can use a full pack of CR123As, which does nothing to reduce my confusion about the battery situation. Anyways, that’s a monstrous light. Note that it’s about a kilo w/ batteries, and probably about 1.5 kilos with the extra battery kit. But wait, there’s even more! Apparently the extended handle kits can stack, as the extra battery carriers are just stacked in parallel, so you could screw three of them onto the end of your light for 16x 18650 capacity and have it double as a walking stick! (Seriously, just run it with 4x 18650 and carry spare cells if you want extra runtime.)
It’s also important to understand that you don’t see lumens per se. You see lux. Lumen output is a measure of how many photons in total are emitted by a light. What your eyes actually see is the number of photons reflected by a given surface. Focus 100 lumens on a small area and it will be dazzlingly bright, where 1600 lumens with no focus at all will be, well, exactly like a 100w incandescent bulb. Your TK76 there has three LEDs of approximately 900 lumen output, but each will behave very differently. One is a 120 degree flood, the second a 60 degree flood, and the third an extremely focused spotlight. The light only outputs 2800 lumens with all three lit, so you’d have a fairly soft diffuse light cast on pretty much everything in front of you, a noticeably brighter but still not dazzling cone in the center of that, and a blinding spot directly in front of you.
For reference, ye old school 2-D cell Ray-O-Vac puts out about 30 lumens. My own “best flashlight” is a single-18650 light with a regular mode of about 30 lumens and a brighter mode in the 300 lumen range (and a lower 1-5 lumen mode is nice as well). 30 lumens is nice for most close illumination needs, while 300 will light things nicely at a moderate distance. 300 lumens at close range is actually uncomfortably bright. A single 18650 cell will sustain a 300 lumen output for a couple hours, and a 30 lumen output all day and then some.
Finally, if you really want informed flashlight advice I’d recommend asking on candlepowerforums.com or budgetlightforum.com, though in both cases I think you’d likely be assumed to be trolling if you started a thread with your original post here.
*Checked a review of this light and apparently (and unusually) it doesn’t step down the turbo output, but the guy couldn’t hold on to the light after about 20 minutes because it became too hot to touch. Perhaps doubles as an emergency cookstove?
