Will the 21-70 Battery (a.k.a. 21700) Replace 18650?

Springs can take up the 5mm slack along the longitudinal axis, and all anyone needs to do is make battery-tubes bigger by 3mm (1.5mm “wrap” would take care of rattling 18650s).

The same way a tube that takes an 18350 can also accommodate 16340s with a little slop, the same can be done for 18650s vs 20700s/21700s.

Don’t want rattles, a bit of construction-paper wrapped around an 18650 can cure that.

Don’t see what the problem is, just need flashlight mfrs to get on board.

Assuming it’s true, it’s still not as high capacity as 26650 (5500 mAh Shockli), but is nevertheless more efficient on per-volume basis. On par with 18650. And really looks like a great choice for pocket rockets.

You do realize that this graph still shows “hundreds” of cycles, not “thousands” right? :wink:

Somebody mentioned flashlights that come with 3×AAA adapters. They are a bit larger than 18650, aren't they? Would 21700 fit?

Personally, I prefer 26650 size over the thinner 18650. If large efforts are put into developing 21700 cells with >4500mAh, then those would be better than 26650 in every way. This is what I hope will happen

The formula for fitting 3 small circles with diameter d in a bigger circle with diameter D is: D = d * (1 + 2/√3).
Or to put it in plain numbers: D = d * 2.1547.
Because the diameter of an AAA cell is 10.5mm, you need 22.62mm for an AAA adapter to fit in.
That should be enough for a 21700 to fit in.

Yes, but they will obviously last that long since they have retained so much of their capacity after hundreds of cycles. Even the worst one is still above 85%!
The main thing that makes a difference is not fully charging them and not discharging them all the way to 0%. The other thing is the active cooling. They never get hot.

But AAA is 26 mm too short, which adds problems of its own. Nevertheless, good call with 3xAAA.

The AAA carrier makes up the difference in length. I have several lights that take AAA or an 18650. They should also work fine with a 21700.

Crap, they found it (the new Bakken) just before I’d posted that upthread! 2nd largest oil field in the world behind the massive Gahwar field in Saudi Arabia. Just found it in Texas no less! “Huge new oil and gas find in the Permian Basin in west Texas

Suspect that will both secure the US as a dominate oil supplier for many years, and slow the rapid acceptance of battery powered cars. How much it slows it remains to be seen, The new Tesla model 3 has like 400,000 some odd pre-orders it’s been said.

IMR has the Samsung 21700’s https://www.imrbatteries.com/samsung-48g-21700-4800mah-flat-top-battery/?mc_cid=8a30e27acb&mc_eid=75ac41df2e

Great find!

Thanks! I’ve needed a 21700 to check tune sizing on my scratch build, ordered 2 of those. 4.8Ah is not too bad for the 21700 form factor! Even if it is a ~10A max continuous discharge.

IMR has 21700 IJOY’s (40amp pulse) now…https://www.imrbatteries.com/ijoy-21700-3750mah-flat-top-battery/?mc_cid=91754df226&mc_eid=75ac41df2e

Heh-heh, we got the same email… :smiley:

Samsung 48G test by Mooch

21700 is the future IMHO. Small increase in size for big gains in everything else.

Indeed. Volumetric efficiency (power/size, capacity/size) seems slightly lower than that of 18650. I assume it’s temporary, it should be actually a tad higher. But when considering efficiency of the entire flashlight, they are often better already. But the flashlights haven’t arrived yet…I would love to get an Emisar D4 in 21700. Since the head is larger than battery tube, total size increase would be tiny. Battery would have 40% more juice than GA with about the same power.

Yeah, they should be reaching ~5500-5800ma according to the data I saw last year. Course they only started making these batteries last year, so they are doing ok for such a short development time so far.

With continuous discharge max set around 10A and recommended 4.8A for optimum life, I don’t see these being great for flashlights. The testing I’ve seen to date show an immediate drop to 3.7V when under load, by the time our low voltage protection kicks in they’re only giving 2000mAh capacity (in testing)

I-Joy rates a 40A pulse, which means they too won’t do a continuous discharge rate for say, a triple XP-L. Or even a Luminus SBT-70 for that matter, one, all by itself. So I’m not hedging any bets for these Tesla sized cells to take over our world anytime soon. And besides, carrying extra cells would be all the more difficult due to their sheer size factor.

I got the notifications about the new offerings just like y’all did, but opted out as they won’t run my lights built for the big cells. I need 25-30A continuous, not seeing any of these that will do that. (an Efest 20700 will though….)

Disregard the I-Joys. If you want capacity, 48G will run at nice output (350 mA) for over 13 hours. Often enough for a weekend without carrying spares. According to Mooch, it handles current just like your 20700B does, which is enough for many uses. It may not live forever when overdriven. Oh well…
If you want power, 30T is scheduled for the next year and it’s a good deal more powerful than VTC5A. Or Efest 20700 for this matter.