why the popularity of 26650 cells and bigger in flashlights?

I really like the 18650 size battery because of its high capacity, and it comes in high quality, many brands and different types for a good price. I have done a quick search on some available 26650 cells, and they look inferior to 18650's: they have twice the volume, but not quite twice the capacity or discharge current. So why choose flashlights with this battery if there are options for 2x18650?

Just curious, if the reasons are convincing, I am happy to go into 26650 flashlights :-) .

Best reason I know of to go with the bigger cell. The 26650’s with high discharge rates give more current longer when a heavy demand is called for. If you’re driving an XM-L2 at very high amperages the Vf doesn’t allow many if any current 18650’s to play.

But two 18650's parallel perform better than one 26650, right? (or wrong?), so I would then design a flashlight around twice as many parallel 18650's.

I really prefer the size of 26650 battery tubes in the hand. DBC hit on the biggest "real" issue that I'm aware of. I would really like to see more 26650 cell optios, especially from better know manufactures and increased capacities.


I’m the same as Gary, I like the increased tube diameter and heft of a 26650 or bigger light, I can always run them on 18650 cells if I wish but its hard getting a 26650 in an 18650 tube.

Reason #1 is less voltage sag at higher current draw. Reason #2 is increased capacity. Yes the volume might be double that of an 18650 but outer dimensions are not double. They are only 4mm 8mm wider and the same length. 4200mA capacity compared to 3000mA.

As they get more popular the manufacturers will increase the density of them as they have with 18650 cells. Remember that 18650 cells started out around 2000mA and are now up to 3400mA with even greater to be released in the near future. If the makers use the same production techniques with the 26650 we should easily see 6000mA or more from them. For a cell only 8mm wider than an 18650 I'd say that's a huge step up for very little extra size. Right now most people still don't even know they exist. As they become more popular they will grow in capacity.

Two cells, do you have to make sure they are matched and take more care when charging/discharging? One slightly larger cell seems neater than two.

26mm - 18mm = 4mm??

Otherwise I agree with you. :)

I hope they get a better capacity, I get the impression that 18650 is getting even more mainstream, and not this size.

I'm not sure if you meant exactly this, but I guess you have a point referring to the outer dimensions, two cells next to each other create some unused space, you may have to add that to the practical size of two cells together, if you look at it this way, two 18650's are bigger than one 26650 :

He meant 4mm wider on each side :) .


I only have a couple of 26650 lights so far. But for me one thing I like is the overall size.

For example the BLF A8 is about the same length and head diameter as a L2M is. The only difference is the body of the A8 isn’t any slimmer. But in real terms it needs pretty much the same space in a pocket and identical space in a holster.

In return I get longer runtimes and more time at max output due to less voltage sag.

One, two or three 26650s are also easier to handle and maintain than two, four or six 18650’s. I have a TK-45 (8xAA) that I seldom use because dealing with 8 cells is annoying and time consuming. This is secondary to benefits mentioned above, and I know it may seem trivial, but ease of use is a factor for me.

Doh! :zipper_mouth_face: Thanks! For some reason when I was doing my calculation 22mm kept insisting itself instead of 26. I’ve corrected it. I still agree with my original opinions. :smiley:

You could always design the light around double 18650’s, then worry about one making the other explode, or just use a single 26650 and be much safer and neater. I too like the tube diameter of a light designed for the 26650, like the HD2010…something about it’s proportions draws me to that light….now if it could only be MADE better.

I would love to see Solarforce make a HD2010 style light using the 26650 format. HA Type III on excellent machining in the HD2010 format would be a killer combination!

Is the significantly increased output and runtime for the below modded DST.

In Xml2 especially.

I’m sold on 26650’s. IMO highly underrated.

To me, it seems 3P3S (or any xPxS) would be safer than 3S. Especially, if the parallel banks are connected at the 3P1S level.

Lets say you have a cell go bad while sitting in your light. This should be very rare if you check your cells each time you charge, but lets say it happens anyway. If the cell has a parallel cell or cells, those remaining good cells will help keep it's voltage up and help compensate for it while running.

Another reason to go 26650 rather than multiple 18650 is that some of us would rather avoid LiCo or simply want to take advantage of the other advantages of alternative chemistries (such as higher current or longer life). High capacity 18650s are the exclusive domain of LiCo. Safer chemistries such as LiMn and LiFe are MUCH lower in capacity in the 18650 size. But when you step up to a 26650, you not only gain capacity by virtue of the larger size. But capacity increases MUCH more proportionately to size with LiMn and LiFe than with LiCo. In other words, while a LiCo 18650 has a much higher capacity than a LiMn or LiFe 18650, a LiMn or LiFe 26650 comes close to or equals the capacity of a LiCo 26650.

i like the higher capacity of the 26650s, and now the even larger ( Close to D-size diameter) 32650s are even gaining some interest.

I was looking for someone to say that. The Tesla Roadster uses 18650 cells (as well as huge amounts of coal and uranium to generate the electricity, lol), but they have a good chance to match them and balance them.

In my tests, the KK ICR 4200 from FFL/CNQ beats the KK ICR 4000 in current it can generate for a high amp XM-L2 build. As you guys have been saying, sustained high current, high voltage draw is the 26650 advantage. I have 3 SONY 50A 26650 cells on order - will see if they out perform the KK 4200. HKJ published the internal resistance of a KK ICR the same as the Samsung INR 20R (0.04 ohms), so you get basically double the capacity for the same power, but it also definitely sustains the high power longer than the Sam 20R.

Edit Correction: Crap!! my bad! HKJ had the KK ICR 4000 at 0.05 ohms, and the Sam 20R at 0.04 ohms, while the SONY 26650 he published at 0.04 ohms internal resistance -- same as the Sam 20R. I suspect the KK ICR 4200 is better than the 4000, so it seems like it may be all even with the Sam 20R and the SONY.