18650 / 21700 / 26650 ... what size of Li-Ion Batt to "keep"?

Poppy

Flashaholic
Joined
Dec 20, 2012
Messages
8,315
Location
Northern New Jersey
Oh it's a custom. Ok ya I would need to drill and tap the tail cap
No need to drill and tap. That clip is bolt on and it comes with little bolts. You use the pre drilled holes for the lanyard.

1699757940370.png
 

blah9

Flashlight Enthusiast
Joined
Mar 10, 2011
Messages
2,105
I also agree that 21700s are awesome. I only have one light with them, and I love it. I think I will stick with that format going forward, at least for the most part. I like the increased runtimes and the way the light feels in my hand better than the 18650 lights.

It might also seem crazy, but I EDC my 21700 light pocket-clipped into my front pocket. It indeed is pretty large, but I personally like to have all that power with me whenever I need it. This is the Fenix TK22 TAC by the way.
 

yellow

Flashlight Enthusiast
Joined
Oct 31, 2002
Messages
4,624
Location
Baden.at
The opinions more or less what I thought,
think I might give an 21700 model a try
(but still stay at 1*18650 (+ a spare cell, if possibly needed) as primary setup
:)
 

Poppy

Flashaholic
Joined
Dec 20, 2012
Messages
8,315
Location
Northern New Jersey
Yes it is. Any 7135 based driver can run on 2 cr123a. It's not the most efficient, but it'll run fine. As long as you're not pushing output as cr123s don't care for going over 2.5a very much
I was sure that I read on the Convoy site years ago that the S2+ was not compatible with 2 CR123 batteries. Perhaps they stated that it is not compatible with 2 RCR123 cells?

What I read here the AMC7135 drivers can handle 7 v max. 2 X RCR123's fully charged would be above 8V.
 

vicv

Flashlight Enthusiast
Joined
Mar 22, 2013
Messages
2,733
Location
Southern Ontario
So I updated saying I was wrong and it didn't work. But I was wrong about that. So deleted those posts to reduce confusion. Lol. Somehow I got my light switched to mode 1. That has strobe and all the blinks modes. No idea how. So that was the erratic behavior I was seeing. Got it switched back to mode 2, and everything is well. Played around for about 5 minutes with fresh cr123a and all levels are working exactly as with a lithium ion.
 

Monocrom

Flashaholic
Joined
Aug 27, 2006
Messages
19,559
Location
NYC
I also agree that 21700s are awesome. I only have one light with them, and I love it. I think I will stick with that format going forward, at least for the most part. I like the increased runtimes and the way the light feels in my hand better than the 18650 lights.

It might also seem crazy, but I EDC my 21700 light pocket-clipped into my front pocket. It indeed is pretty large, but I personally like to have all that power with me whenever I need it. This is the Fenix TK22 TAC by the way.
Not that crazy. My Nitecore MH12S has found its way to my front pants pocket. Not my first 21700 light I've clip-carried. Likely not the last one either.
 

chaosdsm

Enlightened
Joined
Feb 11, 2014
Messages
281
Location
Florida
Hi.
1st off, I am totally into 1*18650,
and like the lights' size format the most.
+ think to be better off with an additional spare cell in regard to a bigger light with larger cell
+ the larger cells I had so far - 26500 and 26650 - simply were on the lowest end of quality.
.
So, question:
for that one additional "bigger" light,
for "thinking into the future"
what cell might be best to plan?
21700
26650
32650
even a different one to these 3 ?
For my hands, I prefer a flashlight that uses a single 26650 cell. Not to heavy, fits my hands well, and has better capacity than 18650. While a 18650 based flashlight is to small for my preference.

21700 in theory should be the cell size of the future, capacity equal to 26650 in a smaller overall form factor, a usually lower price, & which should fit well even in small hands. I'm personally moving from 18650 to 21700 because 26650 based lights & batteries tend to be a little more expensive, and half of my lights are used by other people who think the 26650 lights are to big.
 

jtr1962

Flashaholic
Joined
Nov 22, 2003
Messages
7,502
Location
Flushing, NY
If you want to go with safer LiFePO4 then 26650. The 18650s in that chemistry are too low in capacity. We're up to 3800 mAh in the 26650 size however.

If you want to stick to regular li-ion, then 21700. At least 50% more capacity than 18650 but still a manageable size.

Since sodium-ion is starting to become commercially available I'll give similar recommendations for that as for LiFePO4. Go with 26650 or 26700, not 18650. Actually, 26700 is all I've seen so far in the 26mm diameter. Rated capacity is supposedly 3500 mAh, but remember these are first generation cells. I expect we'll get past 5000 mAh within a year or two. And they should eventually be dirt cheap compared to any lithium chemistries. Nice things about sodium-ion are the cold weather performance ( ~90% capacity at -20°C), the inherent safety, plus you can run them down to 0V without destroying them.
 

Mike G

Newly Enlightened
Joined
Jan 25, 2022
Messages
57
Location
Canada
Sodium-ion, eh? First I've heard of 'em. More familiar with sodium-iodine. I will definitely be listening for more... I do like me some salt.

How's their cycle endurance and self-discharge?
 

jtr1962

Flashaholic
Joined
Nov 22, 2003
Messages
7,502
Location
Flushing, NY
Sodium-ion, eh? First I've heard of 'em. More familiar with sodium-iodine. I will definitely be listening for more... I do like me some salt.

How's their cycle endurance and self-discharge?
Endurance is supposedly upwards of 3,000 cycles. I'm guessing self-discharge is on par with lithium cells as the basic chemistry/construction is very similar, other than the substitution of sodium for lithium.

I have ten of the 26700 cells on the way. I'll do a complete test and post the results in a new thread.
 

Mike G

Newly Enlightened
Joined
Jan 25, 2022
Messages
57
Location
Canada
3,000 cycles is more than Li-Fe if I'm not mistaken, very impressive if true. If it's also got a flat discharge curve and can handle high amps like Li-Fe, that'd be the cherry on top. That'd pretty much make it the NiMH of 3.7v secondary chemistries.
 
Last edited:

jtr1962

Flashaholic
Joined
Nov 22, 2003
Messages
7,502
Location
Flushing, NY
3,000 cycles is more than Li-Fe if I'm not mistaken, very impressive if true. If it's also got a flat discharge curve and can handle high amps like Li-Fe, that'd be the cherry on top. That'd pretty much make it the NiMH of 3.7v secondary chemistries.
Unfortunately it has a very steep discharge curve (from ~4.0V down to 1.5 to 2.0V). Average voltage is 3.1V, very similar to the average voltage of LFP. It should be capable of high amps. So basically all the good characteristics of LFP, except for the flat discharge curve, but eventually at a much lower price ( <$30/kW-hr ), plus the potential to reach energy densities greater than LFP. Right now CATL is making sodium-ion cells around 160 Wh/kg. This is about the same as their LFP. They're going to 200 Wh/kg next year, with 230 in the pipeline. Currently the best standard li-ion chemistries are around 270. I think it's great we're already matching LFP with the first cells out the door.

The steep discharge curve shouldn't be an issue with today's regulators. Moreover, that makes it easier to calculate the SOC.
 

Mike G

Newly Enlightened
Joined
Jan 25, 2022
Messages
57
Location
Canada
Time will tell, I suppose. Steep discharge doesn't bode well in my eyes. I remember the days when the most you'd get out of your batteries in a flashlight was, what... a quarter, maybe a half of their capacity? At which point the light had gone dim enough to warrant a fresh set, even though you still technically had a good amount of juice left. If I'm not mistaken, most emitters still operate at lower brightness when driven at lower voltage. I know the Malkoffs do. Not very much I suppose, but it's there. Dropping down to half, maybe even less than half of nominal voltage, and starting about a full volt above nominal to boot, seems rough to me. But I guess we'll see how it goes soon enough.
 

PaladinNO

Newly Enlightened
Joined
Jun 22, 2017
Messages
178
Location
Norway
I thought the 26650 was to be the 18650's bigger brother, so I started rotating towards the 26650 for the more powerful EDC lights (~3000 Lumens vs. ~1000 Lumens).
...Not long after (luckily before I dug myself too deep into the 26650), the 21700 comes along with about the same mAh (~5000 mAh), but with smaller size. And now I barely see a 26650 compatible light anymore, it's almost all 21700.

So my 2 Cents is keep both 18650 (more pocketable) and 21700 (more powerful), depending on your needs, but skip the 26650.
 

jtr1962

Flashaholic
Joined
Nov 22, 2003
Messages
7,502
Location
Flushing, NY
Time will tell, I suppose. Steep discharge doesn't bode well in my eyes. I remember the days when the most you'd get out of your batteries in a flashlight was, what... a quarter, maybe a half of their capacity? At which point the light had gone dim enough to warrant a fresh set, even though you still technically had a good amount of juice left. If I'm not mistaken, most emitters still operate at lower brightness when driven at lower voltage. I know the Malkoffs do. Not very much I suppose, but it's there. Dropping down to half, maybe even less than half of nominal voltage, and starting about a full volt above nominal to boot, seems rough to me. But I guess we'll see how it goes soon enough.
It's almost a given that you need a regulator of sorts for most cell chemistries. For one-cell sodium-ion lights you would need a buck-boost regulator, so it's probably not ideal. Two cells and over, a buck regulator can easily deal with the voltage range.

LFP is really the only chemistry I would be comfortable running without a regulator. Figure it'll be between 3.2V and 3.3V most of the time. The resistance in the light should probably drop that to high 2s to maybe very low 3s. That's right around where most emitters sit. By the time the cell drops enough for the LED to dim noticeably, it probably has only 10% left.

There may well be slight tweaks which keep the discharge curve flatter. It would be great if sodium-ion could match LFP closely enough to be a drop-in replacement. The cycle life especially seems really great. The fact they're this good in their infancy is very promising. Can't wait to see where they are in a few years.
 

vicv

Flashlight Enthusiast
Joined
Mar 22, 2013
Messages
2,733
Location
Southern Ontario
Time will tell, I suppose. Steep discharge doesn't bode well in my eyes. I remember the days when the most you'd get out of your batteries in a flashlight was, what... a quarter, maybe a half of their capacity? At which point the light had gone dim enough to warrant a fresh set, even though you still technically had a good amount of juice left. If I'm not mistaken, most emitters still operate at lower brightness when driven at lower voltage. I know the Malkoffs do. Not very much I suppose, but it's there. Dropping down to half, maybe even less than half of nominal voltage, and starting about a full volt above nominal to boot, seems rough to me. But I guess we'll see how it goes soon enough.
That's driver choice for the malkoff. And what you're talking about is alkaline batteries in incandescent lights. They alway sucked. Regular lithium ion cells have a pretty steep discharge curve, and they're great for modern incandescent lights. Not as good as lifepo4, but not many bulbs work with the voltages of lifepo4 chemistry.
 

Latest posts

Top