21700 vs 18650 battery format

I recently watched a thread that started about how the future of Lithium cells was 21700 format cells. It then completely digressed into a debate about how to calculate volumes and percentages. It got so bad that it was soon closed down due to it being totally non constructive. I’m not trying to restart that thread to create another pointless debate but wanted to point out that it doesn’t matter what size you choose they are all Li-ion cells with the same active materials. Yes there are different combinations of chemicals for different properties and preferences by different manufacturers but the size of the can doesn’t alter the chemistry. Therefore it boils down to what size cell you can fit into your enclosure to get the voltage you need and the highest Amp hours you can. The newer formats do tend to be more expensive per w/h but this is usually due to manufacturing costs. 18650’s are the cheapest because they are mass produced, the other sizes will change in price as more and more are produced. In theory a larger can format will have higher energy to total volume due to the fact that there is more active material to can material compared to a smaller can size, the increase though is very small. We have had different size Alkaline batteries for years, AAA,AA,C and D people don’t say “D cells are better than C cells” Yes they have more energy but that’s obvious because they are bigger. If your torch doesn’t fit D cells then the argument is mute. Same applies to 18650 vs 21700.


I agree, I chose Samsung 30Q because they have a pink wrapper.

Does anyone know what the best kind of motor oil I should put in my car?


Is this a rhetorical question or for real?


Haven’t decided yet.

1 Like

The one in the biggest can is best.


Dont know why its the case, but 21700’s are more power (max continuous power output) and energy (total capacity in W*h) dense according to the spec sheets. Enclosures and cost aside, agreed that 21700s are better

|Description|A123 ANR26650M1A|A123 18650 LIFEPO| |Max Continuous Amperage (A)|70|30| |Voltage|3.2|3.2| |Weight (g)|76|39| |Capacity (mAh)|2300|1100| |Cell Power (W)|224|96| |Power density (W/g)|2.947368421|2.461538462| |Cell Capacity (Wh)|7.36|3.52| |Capacity Density (Wh/g)|0.09684210526|0.09025641026|

1 Like

Well confused with that one? We are talking about 21700 vs 18650 Li-ion cells and you put up specs for 26650 and 18650 LiFePO4 cells which are completely different chemistry. If you want to know more about Lithium cells try this: https://marsen.com.au/lithium-explained/what-are-lithium-batteries/

It’s a side by side comparison of a123’s lifepo cells, in their 21700 format (which boosted uses) and 18650 format. Same chemistry, same manufacturer, different format

Ok I see. The 26650 cell is quite a bit bigger than an 18650 cell. These two one is 76g and the other 39g almost twice the size.(weight) But yes as you get bigger the power density increases, in this case from 2.947W/g compared to 2.4615W/g.

A123 don’t manufacture 21700 cells, Boosted do not use 21700 cells because they use A123 cells and they don’t manufacture 21700 cells.

26650 is not 21700 (quite a big difference)


Please don’t get this started again. Not all 21700 have a higher energy density than 18650 just like there are 18650 with various capacities out there. Right now top of the line cells in both formats are VERY close in their density so there is not really a difference between them besides the size USUALLY favoring 18650 (as you reach the desired S count in less space).

Advantages of 21700 are high current capabilities (just like top of the line 18650) and high cycle life. Downsides are price and their size and weight.

Now everybody needs to decide for themselves what compromise they want to make. In 5 years when 21700 have become like half the price and have higher capacities than today we all might switch to 21700 but until then 18650 are the better choice most of the time.


So I did the calculations in the old thread on the samsung 40t vs 30q.

And what I found was that the 18650 packed more kWh by volume AND weight. Maxid also discovered that you pay less per kWh with the 18650. What that means is if size/space constraint AND cost is important to you, the 18650 format is best for you. You get more “bang for your buck” so to say.

However, while you get better cost/space concerns with the 18650, the 21700 still has more raw energy, just due to its bigger size. Also, they generally have a higher continuous discharge rate which is important for high drain application like esk8.

No one was saying its wrong to use 21700s, for some who have a ginormous enclosure and money to blow and need the most range they can get, they are absolutely the best choice. We were saying it was wrong to choose them if you wanted the most energy for every dollar/inch in your enclosure, which the original poster of the previous thread contested… and that led to the consequent shitshow.

Maybe there is a 21700 out there that beats out the 30q on space/money. I just went with the 40t for the comparison because that was what seemed like the best performing one on mooches battery test linked in the old thread.

No one knows your build better than yourself so you have to do your own research and decide…


just cram in some bulldozer grease and it should run fine :wink:

Did you do the calculation to know when 21700 is competitive against 18650.

The best thing for us about 21700 is to people start to crash their Model 3 and the battery’s end up in eBay

With time it will be a cheap source for them

1 Like

The tesla 2170 cell may be great… may be just anouther 21700. I dont hink anyone has tested it yet publicly, at least not that i have seen… and to the OP… you obv didnt read the whole closed thread, or any thread on this subject…Unless you really need the amps, or just like spending more money on cells, the 30q is tops on kWh in volume and weight when compared. At least to the 40t. As that is what was brought up.

We know it’s roughly 5 Ah and that can take a burst of approximately 20A, but I agree, more testing is needed

Ah, my mistake, not 21700, they’re 26650. But still, more specific power and energy than comparable 18650 cells

This is dependent on Tesla not going bankrupt.

Prob not gonna happen. Plus panasonic will still push the new battery… samsung already anounced there copy… after they get one, disect and copy it.

1 Like