18500 vs. 18650

As most here know, battery coding nomenclature denotes first 2 digits as diameter and next 2 digits as length, in millimeters. So an 18650 is just 15mm longer than an 18500. 1.5 centimeters, a little over 1/2 an inch.

In terms of flashlights, this size difference doesn’t seem very remarkable at all. And, in checking up on the upper limit of mAh for these two types in the retail market, it seems to be about a 1000mAh difference in favor of the 18650. And then, in terms of purchase price, it looks like they average about the same. I can understand the 18350… as that’s a good 30mm, over an inch in length shorter than the 18650.

So why do people bother with 18500 cells in flashlights?

I mostly like 18650 and 21700 cells because they have a lot of mAh per volume.

Size. Sometimes you design a light to a certain size with the idea of stuffing in the biggest battery that will fit.

I believe 18500. 20350 and 20700 were primarily used and pushed during the vaping revolution. Manufacturers such as IJoy and others used these lesser know cell sizes because they were very cheap to get, therefore popularizing the weird sizes more.

Same here.

Just to loop back to my previous point, 15mm is a 30% reduction from an 18500 to 18350, while 15mm off 18650 to 18500 is a 23% reduction. However... from a recent scan of cells available, it looks like the top end of an 18350 cell is 1400mAh. Best 18500 I've found is 2040mAh, AND it's cheaper than the 18350 cell by about $2.

So I guess I kind of answered my own question. Cost, size and mAh ratios can work out in favor of one or the other. And some people may put a premium on the best size/mAh ratio.

Yeah, for vaping I could also see weight and size being a factor, and the 18500 kind of fits a certain “comfort factor” versus a larger 18650.

Size and weight

  • Sometimes an 18650 light is just a bit too long. Being able to cut out 15mm can actually make a difference. A shorter light is easier to pocket.
  • A light that weighs less is less noticeable in the pocket or clipped to a belt.
  • I can tell the difference between 18500 and 18650 when I EDC. Sometimes I prefer the extra capacity of 18650, other times I prefer the size and weight savings of 18500.
  • The highest capacity high-drain 18500 that I know of is the 2200 mAh Vapcell L22. Its capacity isn’t that much lower than a 3000 mAh Sony VTC6.
  • The best 18500 has twice the capacity of the best 18350 and is only a little longer. Also I find in some lights 18350 is just a bit too short to comfortably hold in the hand (FW3A and Emisar D4). Using the 18500 tube is more comfortable.

Thanks! Interesting to see that, Vapcell L22. Best price I could find with shipping worked out to $8 a piece, 2 minimum. But when able to buy an 18650 with 3200mAh for $5, not great!
Btw, I spied a Vapcell 18350 listed stating 3500mAh. Is this some newfangled battery chemistry, or exaggerated capacity? Of course, price per cell is $12.50, which blows the comparative value proposition.

Sounds mislabeled. They probably meant to write “18650”.

I for one ordered a couple of 18500s to replace the 3 x AAAs cartridge in some cheap lights. Never use them nowadays. They were not high capacity (PK Cell 1400Wh – whatever that would be in Ah).

As vonroyale pointed out, some oddball sizes. Never heard of the 20350.
The 20700 cell caught my curiosity. I had ordered one but it’s diminishing returns – capacity comparable to a 18650 cell but oversized and doesn’t fit. Molicel 20700 (P30A?) at 3000 mAh.

That is over 25% less capacity.

  • Yup. And it is a significant difference. For 15mm you lose over 25% capacity.
  • But then compare to an 18350…. for 15mm you gain 100% capacity.
  • It really comes down to personal preference. An 18500 certainly does not have the capacity of an 18650. Nor can it sustain as high lumens. On the other hand, it has a lot more capacity than an 18350, 14500 or 16340. And going the other way, an 18650 does not have the capacity of a 21700 or 26650.
  • As a flashaholic, I appreciate the wide variety of available cell sizes. Having a choice is nice.

I really like subbing 18500’s for 3xAA.

18500's really don't substitute for 3AAA's very well , They are always a little too short .

I use them because i found a bunch of sanyo's in old camera rechargable packs a long time ago .

I bought the 18500 body tube for the D4 and would agree with Flashlight2 that it's generally a matter of feel . Sometimes a 18350 just feels a little too short . Everyone seems to like the length of AA flashlights .

2x18500 replaces 3xCR123A, which are 34mm each, and nominally 3v to the 18500 4.2v so most lights stock drivers accept the change fine. It was a mod that used to be done to Surefire 9Ps and similar lights.

A long, long time ago. I myself did a mod of a Pentagonlight L3 which involved boring the body (with a handdrill!) to 23/32” to accept 2x18500 cells and replacing the stock Lux V with a custom bin Lux V WW0T emitter from the Sandwhich Shoppe. The LED itself cost $44.00 and was pumping out a serious 100 lumens at 600mah. Seems like such a waste of time now, but back in 2006 it was a serious upgrade and gave me really good rechargeable lighting capability.

Anyway, that’s the trip down memory lane tonight.

Reading spoonrobot modding adventure/challenge got me thinking how today’s lights will be obsolete in a few years. I’m rather new (about 5 years) to the flashlight crowd, but already some of my lights need upgrades. For the moment there are newer replacement emitters and drivers, but could all change with advancements. The COB is moving well into the single emitter lumen capacity, and we are seeing multi-element dies more often with very good performance.

Just digressing there…

In an S2+, if you use a TIR lens vs the reflector, you can (have to, in fact) squeeze up the pill and that makes the inside roomier. So you can then use the shorty tube with an 18500, but may have to also shorten the springs a bit.

So you’re getting an “18350” light with the capacity of an 18500.

Thanks for the memories. :wink: Pila flashlight owner here, had the GL3 that takes 3xCR123A. I remember the Pila 500 cell where two could replace them (equivalent of 18500).

Well, I was wanting to put a copper 18650 tube on my FW3A without having to just outright buy a whole copper version. But they won’t sell the tube separately (despite offering the aluminum 18650 tube separately). The 18500 tube in copper is $14. They have a Panasonic 18500 with 2040mAh at $6. Actually not all that bad if intended use of the FW3A is anything but generous turbo. Too bad the clip ends up ill fitting, so I’m going to try the deep carry clip and see if that works.

i dunno, i find 18650 has the best balance of features/dollar, in many directions

i think the most development has gone into them, because of electric cars, and vaping


You are correct.

However, 18500 is ideal for those who want something a bit more compact and less weight than 18650, but with more power than 18350.

I have a couple of SHTF P60 lights that I built to use AA or 14500 cells, this takes an adapter tube to account for the diameter decrease of the 14500’s. But, these lights with the existing tube will also run 18500’s. I consider this an advantage as none of them are high current lights.

I do the same. I found some protected 18500 TrustFire cells on clearance for just $2.99 each and bought all their remaining stock which was six batteries. I have them in 2-3 flashlights (that used to take 3 AAAs) and they seem to work well.

I really wish Sofirn would make a 18500 tube for their SP40 headlamp. The 18650 is too bulky and the 18350 shorty is just too small.