What is the best 21700-to-26650 adapter ?

[billyandriam]

Hello to the community! Basically I own an Astrolux FT03S that run natively with 26650 batteries.
Now, I have seen many many people recommend to use the Molicel P42A with 26650 flashlights. The argument is that 21700 can fit into the tube.

Now, I decided to buy the newer Molicel P45B and I am pretty happy with the result. The only thing I realized is that trying to fit 21700 cells into a 26650-sized tube works but the battery wobbles which was to be expected. I have tried to look for 21700-to-26650 adapters everywhere and basically, I only found one seller from Aliexpress who offers this:

This is how it looks in real life and this is how it compares to a 26650 Keeppower cell.

Now the 21700 Molicell+adapter can fit very well into the FT03S except that there is still a small, a small shaking & wobbling sound and the tail of the flashlight when I move it around. I am very curious to know if someone else had to go through the same issue and how they solved this issue. Thanks in advance.

[TARTARA]

Welcome on BLF !

Why you don’t use only 26650… your flashlight was made from these batteries… !?

[Inexorabill]

Sometimes lights rattle even with the correct battery in them. You might be able to shim it with paper or tape or something so it fits tighter and doesn’t wiggle as much.

[TARTARA]

Don’t listen anyone…
We are taking about 5mm more (in the best case scenario) ! If it doesn’t fit don’t try to make any modifications, your flashlight was made for 26650 batteries, and probably you gonna make damage on your flight because of some “experts”… !?

[Marc_E]

I would guess it’s the adapter moving rather than the battery, the springs would be holding the battery in place to a degree while the adapter is free to move around, including up and down as it is shorter than the tube (the length of the tube incorporates the battery and springs).

Either look at filling the gap between the adapter and battery, or the adapter and tube, with paper/cardboard/anything you can think to wedge the adapter in place, or look at ditching the adapter altogether in favour of a couple of o-rings to roll onto the battery.

[SIGShooter]

I use o-rings on 21700’s when I’m using them in my one and only 26650 light.

[SIGShooter]

@TARTARA

Don’t listen anyone…
We are taking about 5mm more (in the best case scenario) ! If it doesn’t fit don’t try to make any modifications, your flashlight was made for 26650 batteries, and probably you gonna make damage on your flight because of some “experts”… !?

Does Astrolux count as experts? This is what they have posted on their page for the light.

From this page:

Astrolux® FT03S SFH55 9300LM 924M Anduril UI High Lumen Powerful Flashlight...

[Mandrake50]

@Marc_E

look at ditching the adapter altogether in favour of a couple of o-rings to roll onto the battery.

I think that this is the best solution. I just have not found the correct size O-rings. I use them for 18650 to 21700 conversion. I have gotten a few sets with different lights. But I haven’t found a good size for 26650 to 21700 adaption. Anyone knowing the right size (Something that is snug on the 21700, holds the cell without rattling, and allows it to be put in and taken out easily), I would love to know.
With the correct size O-rings, there is very little likelihood of damaging the light. Obviously some care needs to be taken. If the tail cap can’t be tightened all of the way, or it starts to crush the ends of the 21700 cell, just don’t do it. Go slow, and check as you go.

[d_t_a]

I bought these some time ago to try. (Convoy 21700-to-26650 o-ring)

https://www.aliexpress.us/item/3256802772572245.html

So far they seem to work (I haven’t checked on many different flashlights).

I did try on some 21700 batteries, and what I noticed is that 21700 batteries with the correct diameter (around 21.0-21.2mm) will fit nicely into them, and converts them to be usable on 26650 flashlights (assuming height requirement of the 26650 flashlight will accommodate the longer 21700 battery). Eg. Molicell P42A, Samsung 40T, Tesla Model 3 21700. (I haven’t have a way to purchase Molicell P45B shipped to my country at a reasonable price, so I haven’t gotten a P45B yet)

However, using these o-rings on “slightly-wider-diameter” 21700 batteries (eg. Lishen LR2170SD, LR2170SA, etc), which measure something like 21.5-21.6mm diameter won’t fit too well on these 21700 o-rings (they can still be used, but the resulting “26650” usually becomes too wide/too tight to fit most 26650 flashlights.

Aside from that, I notice that there are a few 26650 flashlights that don’t fit some 26650 batteries (eg. the first batch of Astrolux EA02’s 26650 tube fits standard “slimmer” 26650 but not “wider” 26650 (example of “wider” 26650 batteries would be the Vapcell/Shockli 5500mAh 26650 (based on PLB 5500mAh). Later batch of EA02 increased the 26650 battery tube diameter so they will fit the Shockli/Vapcell (PLB) 5500mAh 26650.

(Incidentally, the early batch of Maeerxu M8 also has this similar issue of not fitting the “wider” 26650 batteries (although later batch of Maeerxu M8 fits the wider 26650 batteries).

However, the problem is that if the 26650 tube fits the wider 26650 batteries, then their may be some very slight wobble when “slimmer” 26650 batteries are inserted in them.

I think most 26650 flashlights battery tube are now made to accommodate the “wider” 26650 batteries, so if we happen to use the more standard (slimmer) 26650 batteries, there may be some slight wobble (if the tail/head spring are not tight enough).

Going back to the Convoy 21700-to-26650 adapter, it’s then possible that with this adapter, some combination may not fit some 26650 flashlights, but some will.

Hope this info may be useful, although may not exactly be a solution to your question.

[billyandriam]

Hello! Thanks for the warm welcome message.
26650 are great but I just need that extra oomph in order to reach the 9300 lumens which the light was rated for.

No 26650 cells in the market are good enough to drive the light to 9300 lumens.

[Limsup]

Astrolux used to include a similar adapter (26650 to 21700, 18650 adpater), so I think the one shown should work fine.

Oh wait. You already ordered the adapter? If you are worried about the wobble you can wrap some tape around the adapter so you can avoid the rattle.

By the way, I have been happy with the adapter that came with FT02S. The adapter is well made. It looks sturdy and doesn’t flex when I press on it. It has thin o-ring wrapped around the tube so there is no rattle. It weighs around 20g, so it is a little heavy. Maybe it is overkill, but it is the best one I saw so far.

It is a shame they do not include the adapter anymore…

[raccoon]

I read in another thread that this adapter is pretty good…
https://www.aliexpress.com/i/2251832820597519.html

(It looks like the same adapter as in the OP.)

[raccoon]

We’re very glad to have you here, billyandriam!

[Jeffgoldblum]

Guys…
Just wrap some tape around two ends.

Except obviously more tape than that.

The tape is on that battery because i was using it in a convoy with a slightlyyyy wider battery tube than necessary, and as an OCD thing I don’t like leaving room for batteries to rattle around. You will need much more tape than that. But probably not as much as you think.

I use kapton tape because it’s heat resistant, an electrical and thermal insulator, and mostly because it peels off super easy and leaves no residue. So if you want to use the battery for something else later that kapton tape comes right off like it was never there.

[Jeffgoldblum]

@billyandriam

No 26650 cells in the market are good enough to drive the light to 9300 lumens.

They’re sold out right now but you can get them direct from vapcell

Vapcell 26650 32A Flat Top 4200mAh Battery - Genuine

26650 rated for 32a CDR. It doesn’t make sense to me either. But hjk tested that cell and the charts look excellent. Definitely can do 32a continuous discharge. IF, and it’s a big IF, they’re still using the same cell in there.

[SIGShooter]

@TARTARA

Read my post first and then reply to me !

I read your first post and you didn’t answer the OP’s legit question. And it’s not as if the company said that only 26650 batteries can be used in it since they specifically mentioned 21700 and 18650 batteries. They all have the same voltage after all.

Your preference is to use a 26650 battery in the light which is fine. But others (like the OP) may prefer to use other batteries that they might have, can more easily source, etc which is a perfectly reasonable choice.

I’ll readily admit that your second post where you disparaged others for using 21700 batteries in the light struck me as being extremely patronizing.

[Jeffgoldblum]

I saw that post before it disappeared you sneaky sneak.

Making fun of my genius tape strategy… I’ll have you know this is special tape. Kapton tape. It’s used all the time in electronics and around batteries especially. Open up something with a built in pouch cell and there’s most likely kapton tape in there somewhere.

Not like I’m using scotch like some petty criminal

[billyandriam]

I actually did not know that Astrolux/Mateminco included a 21700 in the past. They still included the 18650 adapter but no more 26650-to-21700 unfortunately.
That is why I started this thread. Basically I was just trying to ask if someone around here found other 26650-to-21700 on sale somewhere, especially if those Astrolux adapters are available for sale. I also contacted their Facebook page, but I was left on seen LOL.

I tried the tape wrapping around the bottom edge of my adapter like you advised. So far so good, hope this lasts.

[billyandriam]

Great! I will seriously consider using O-rings for this purpose since many of the comments here suggest this route. Do you have any link where I can buy O-rings that can work as 26650-to-21700 adapters?

[billyandriam]

Great find! Thanks a lot for the link and I am glad to be educated on 21700 cell sizes. I literally never knew that there are size difference even between standard 26650 and 21700 batteries. Thank you for the information.

So, to conclude, these are the options so far when wanting to buy 21700-to-26650 adapters:

1- Buy O-rings from convoy: https://www.aliexpress.us/item/3256802772572245.html (These will work fine on Molicells, Samsung 40T, Tesla Model 3 21700)

2- Buy the 21700-to-26650 which I bought and fill the gap between the dapter and battery with some tapes: https://vi.aliexpress.com/item/1005004662916325.html

3- Try another seller from Aliexpress: https://vi.aliexpress.com/i/33006912271.html

4- Buy older Astrolux 21700 flashlight models like FT02S. Maybe contacting Astrolux directly for making these available for sale but this last option is highly speculative.