21700 vs 18650: Which is the Strongest Electric Skateboard Battery Cell?
Posted by RANDY JEE
I have here, a 21700 battery and a 18650 battery.
First off, it's obvious that the size of the 21700 is much larger than the 18650.
These two are a Samsung 30T 21700 battery and a Samsung 30Q 18650 battery.
Their capacity is 3000mah, so when we use the Samsung 30T 21700 battery and the Samsung 30Q 18650 battery to form the 12S2P battery pack, their voltage and capacity are exactly the same, so the range that can be achieved, is the same.
In conclusion, you may well ask, why does Backfire use a larger, more expensive 21700 battery, but get the same capacity and range as the Samsung 30Q 18650 battery?
The simple answer is that the discharge capacity of the two batteries is different.
- The 30Q 18650 provides 15A continuous current.
- The 30T 21700 provides up to 30A of continuous current, while the Samsung 40T 21700 with G3 PLUS provides up to 35A of continuous current.
If you build a 12S2P battery pack, the maximum sustainable current that the entire battery pack can provide is:
- 30Q 18650 12S2P 259Wh capacity with a 30A maximum sustainable current
- 30T 21700 12S2P 259Wh capacity with a 60A maximum sustainable current
- 40T 21700 12S2P 346Wh capacity with a 70A maximum sustainable current
So the maximum sustainable current that the 21700 battery pack can generate is twice that of the 18650 battery pack.
In simple terms, the greater the current that can be supplied, the greater the power that can be output by the entire electric skateboard.
However, the maximum output current required by most electric skateboards is 30A or less. At first glance, whether the output current of 21700 or 18650 is greater than or equal to 30A, it's irrelevant, but is it?
Let me give a simple example to illustrate this problem.
This is Lily, our Backfire Angel.
This is Aziza, our Designer.
Lili represents the 18650, Aziza represents the 21700.
Lili's best achievement, is to lift a 20kg weight.
Aziza's, is to lift a 40Kg weight.
Let's see them run, carrying identical weights, just like the power output of the two batteries.
So, clearly, Lily has been working at her output limit, very hard, her movements are getting slower and slower, and she's getting hotter, she is actually sweating. But Aziza, conversely, is not tired at all.
The battery is the same. If the maximum current required for the electric skateboard is 30A, but the 18650 30Q battery pack can only output 30A, only at its limit, it will generate heat very quickly, trigger system protection, and often the heat generated, will greatly damage the battery life.
And there will be noticeable voltage sag in the middle, and low battery cycles.
This is why the G2T with 30Q 18650 battery has a governor, which activates when the turbo is engaged. When the turbo is turned on, the speed will continue to rise and break through 42km/h, that's 27mph and the current will reach 30A. If we didn’t make the 30 second limit, combined with the 30 seconds Cool Down Phase, the battery would quickly overheat, causing subsequent damage.
People ask why some brands of turbo do not have a 30-second time limit? Simple! It's because their speed, does not exceed 40km/h, that's 25mph LOL!
However, if 21700 batteries are used, the maximum current required for the electric skateboard is 30A, which is only 50% or less of the capacity of the 21700 battery pack. The 21700 battery pack is not exhausted at all, showing no signs of either overheating, or voltage sag. So the G3 and G3 Plus have NO turbo limit of 30 seconds, subsequently, the speed can now hit, and exceed 46km/h, that’s an incredible 29mph.
So, in final conclusion, the 21700 is an advanced battery, that is inherently optimized for high level electric skateboards.