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

don’t Li-ion have higher energy density then LiFePO4

Very interesting assessment ‘Couchmaster’.
You may very well be on to something, what you say makes a lot of sense. :+1:

One thing is certain…. time will tell. :wink:

The chemistry might in fact turn out to be something entirely new. There are a lot of companies, not just Tesla, tossing large money and a lot of high quality personal at the problem of optimizing power storage in these cells. Tesla was in a race to get product finalized as the development of the batteries was about to head on crash in a race with the development of the gigafactory. They didn’t just try to change the form, but the function as well. They were still testing new cathode material a few weeks before the production was to start I had heard. I suspect that the product they are producing now will be tweaked, modified and improved on a continual basis. I’d love to see a Tesla engineer/chemist share how that went down.

But the Obama administration has also placed a lot of bets on energy via grants. I don’t know what the next administration intends as far as those go but would expect a lot of continuation. I doubt there is a comprehensive list anywhere in the world of everyone who is working on this issue.

Yes, but only last hundreds of cycles compared to thousands for lifepo4.

For something used as often as a vehicle it is nice to not have to spend $5000 on a new battery every few years.

Some test results, at 20A, 30A, and 35A, for the Samsung INR21700-30T can be found here:


In this mini test, it was compared to a Sony 18650 VTC5A and a Sanyo 20700B.

HKJ has posted his more thorough test of the Samsung INR21700-30T:

An impressive battery at high currents.

The thing is it is not just a size game, 26650 never got the attention it need from manufacturer hence it relatively low capability, in theory it should perform much better in capacity and amp draws compared to 18650 but look how much more capacity we gained from 26650? The new Sony 21700 3Tron should be around 5000mah that is as big as 26650 capacity-wise why? because that is where manufacturer now put their research/effort on. So if they leave the 18650 and focus on 21700 i think it is in our best interest that we also starting to use 21700 as a 18650 replacement. As the development on 18650 will be secondary.

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