So the 26650 li-ion batteries are huge and they hold a lot of charge from what I understand.
Does that mean then that the flashlights that utilize them are going to be the strongest since they have more power available?
Sorry if it's a noob question but I am thinking of getting some extra powerful flashlight and just be done with it. Like having a light that can be used for all purposes since it has a lot of power.
Well, “Strongest” is an odd term to use but if you mean will they provide the most output ? then no a 21700 will generally give it higher performance BUT if you mean if it will give you generally the longest runtime on a single cell then yes a 26650 will do the job with a higher capacity.
not really.
usually the cells with a lot of energy storage, are not designed to deliver it quickly
26650s are usually not designed for high max current, rather for max energy storage
so the lumens may not be as much as an 18650 designed for vaping [high max current]
18650s tend to have many options available - the most of any cell type out there currently
No. Multiple-celled lights with batteries in a series (back to back) are strongest because they run higher current and longer. 26650s are same voltage as 18650s, so that wouldn’t make a difference. Only the runtimes would be longer from their higher capacity.
there are different 26650s some are high current, like efest, puts out 30A, others not so much, number of cells and size do not mean much, i have 3x18650 light that only puts out 900lm on paper, solarforce l900 , however i carry noctogon kr4, that runs on 1 18650, night and day difference.
That makes total sense.. thanks for helping me understand.
So I guess I should probably be looking at the 18650 battery flashlight because they are most widely used?
I would say depends on what you plan on using it for but yes the 18650 battery is the most common battery used.
26650 is obsolete, replaceable by 21700 - smaller size and same capacitance.
Whaddya gonna DO wittit?
You need to answer that first before you’d know what’s the best light for you.
yes
define the destination before the route
but i would say right now, 18650 is my favorite cell type
As a rule physically larger batteries will support higher currents. So while not that many 26650’s are designed for higher performance, they will in general out perform most or maybe even all 18650’s.
This really depends on what type of flashlight you are after. Do you want long range or light up a wide area or maybe a mix of both?
Also multi cell/battery lights can offer more performance as they spread the load over more than one battery. But come with the downside of being bigger and heavier.
18650 is currently the most common size. And for me is a great fit for tube style pocket carry lights. But the newer 21700 size (used by Tesla in their EVs) will out perform any of the 18650s. For slightly bigger lights the 21700 is a great choice. But I wouldn’t completely rule out 26650s, but it is a close call between them and a 21700.
If you want a recommendation on a new light. I’m really impressed with the new Astrolux EA01:
There is a group buy were you can get a discount code too if you are interested.
This light is compact and coat pocket friendly. It will run on a 26650, 21700 or an 18650 and comes with the adaptors for the physically smaller batteries. It is also USB rechargeable. So all you need is the light and a battery and you are good to go.
Quality of the batteries tends to play a far bigger role btw. Crap batteries are indeed crap and will give lower outputs and heavily reduced runtimes. Quality batteries are not expensive to buy either. So don’t waste time on slightly cheaper rubbish ones.
For this light I’d recommend something like the Samsung 40T 21700, it will work very well with this light.
The light has a choice of LEDs:
SST-40 - This won’t have the highest output, but will shine a beam further
XHP50.2 - Much more output and will light up a wider area brighter, but will not reach distant objects like the SST-40
Both are good choices. 
Oh so many replies! Now I feel bad for attracting so many people to try and help...
I would like a general purpose flashlight that can illuminate in pitch black conditions so much that you feel like it is daylight :D
Next I want it to last for long. Like at least a couple of hours.
That is why I thought that the 26650 battery powered light would be the best. But I see now from your replies that it doesn't really work that way..
Also it would be great if the flashlight was lightweight and easy to transport.
I think that it should be one of those that can light up a wide field and not focus the light in a single point.
So I assume a 18650 powered flashlight that uses a 3-4 cells that fulfils my criteria would do?
Also, thank you everyone for showing up and helping me! I will be reading all of your replies!
Series doesn’t have an advantage in that regard unless there is a voltage step-up circuit in play (and only then because boost circuits can only step-up so much in proportion to the size of components like the inductor). Running in parallel splits the current load across the cells, running in series reduces the total load (in amps) because you have higher current voltage. What each cell “sees” is effectively the same.
Edit: voltage, not current
i would get a light that uses 1 18650 and carry spare cells
it doesn;t weigh any more and the light is MUCH smaller
wle
There are a lot of great SMALL lights in the 18650 and 21700 size that can light up my acre garden pretty good. They are SMALL and powerful. But the catch 22 on these smaller lights is that they get hot FAST! Thus, most small, high lumen output lights are designed to run a short time (minute or two) then throttle down a pretty good bit: Like from 3k lumens to 500 after the first minute or so.
So if you want a light to light up a 150 yard deep field pretty wide FOR 30 MINUTES, you have to get something larger like my M3c I just got (and need to review). It runs on a 26650 and will run at it’s full output until the battery runs out. Many great ones like it out there too.
If I need a search light, to run in high for hours… multi-cell LARGE lights are what’s needed. Otherwise, a single cell lights is preferred (by me) for any other application.