Anyone who brings up 21700 batteries gets roasted. But why?

21700 batteries are the future for high energy density li-ion batteries. It took awhile but the vape market has almost completely switched over to them with the Samsung 40t being the battery of choice. Obviously esk8 requires more batteries so they are more cost prohibitive. But removing cost from the equation, the 21700 is just a superior cell. I feel like if I build a 18650 pack today I’m using last gen tech, in a few yrs no one will be using 18650s.

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Last time I checked 21700 had worse energy density than 30Q cells plus they are more expensive. The added diameter also makes them worse for slim builds. Don’t really see the benefit compared to top of the line 18650s besides high current capabilities.

What makes the 21700 superior for you?


  • I Don’t Know Jack about batteries but I’ll be following This Thread to learn some things

Efest has a 21700 with an actual tested capacity of 4900mah. These things are barely bigger than a 18650, certainly smaller than two 18650s.

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Just do me a favor and calculate the volumetric energy density for it compared to a Sanyo nga with 3500mAh and Samsung 30Q. Then also do the gravimetric calculation. Let’s talk once we have these numbers.

PS: efest is not a manufacturer AFAIK. They relabel big brand cells. So which cell is it really?

Possibly a Samsung 48g, I realize that but you can’t deny that it got the highest capacity and mooch’s tests are on point. I have both batteries in my hand right now and I can’t tell you the calculations but what I do know is that the size difference is not noticeable and I get at least 30% more battery life out of it.

Edit: Efest is a LG M50

A 48g has a higher voltage drop than a 30Q in the first half of the charge cycle. The difference in size is enormous (~44% in volume). Not sure what’s better with the 48g then besides slightly higher energy density.

Unfortunately lygyte has no test of the M50 so I can’t compare.

I calculate the volume difference at 31.78% where are you getting 44%? And the difference between a 3500mah 18650 and a 4900mah 21700 is 29%.

my thoughts as well :sweat_smile:

Practical examples are key, given 295mm of length to place batteries a single strip of 21700 would give you 68,600mah while 18650 would give you 56000mah.

Something in your calculations must be off then considering a 18650 being 18x65mm and a 2170 being 21x70mm. That makes the 2170 46,4% bigger in volume than the 18650.

Edit The 18650 is 31,6% smaller than the 21700. The 21700 is 46,4% bigger than the 18650 :smile:

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V=πr^2h=π·18^2·65≈66161.94128 V=πr^2h=π·21^2·70≈96980.96522 66161.94128/96980.96522= 0.6822157434

am I missing something?

r is 9 for 18650 and 10,5 for 21700

that would make those cells huge :slight_smile: diameter is 18 and 21, not radius

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You are correct, it’s 2am here need some sleep, regardless given any length a strip of 21700 is significantly more capacity.

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V=πr^2h=π·9^2·65≈16540.48532 V=πr^2h=π·10.5^2·70≈24245.2413 16540.48532/24245.2413=0.6822157435

The result is the same, volume difference of 31.78%

It’s the other way around 242/165

Obviously but length is not all - thickness is also an issue. Plus what voltage would your 295mm battery have compared to one made out of 18650s?

Incorrect, 16540 is 68.22% of 24245. Basic math. Thickness is 3mm different. Voltage is much less of an issue when you are running so many batteries because the voltage stacks.

What? To calculate the size difference I based my numbers on the increase and not decrease. So my numbers are 242/165 which is 146.67% - basic math.

Voltage is an issue as it limits your top speed. What series count do you achieve with your 21700 in 295mm?

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