Vapcell INR18650 2000mAh 38A batteries: are they really the highest-current 18650 cells?

I decided to try some 18650 batteries rated for a maximum continuous current of 38A, just out of curiosity. As far as I know, these may be the highest-current batteries of this size, but it turned out to be a lot more interesting than that.
Inspection, tests, intrigue, investigations, and conclusions.


Let me say right away: these batteries aren't advertised as the highest-current cells, but I haven't seen any mention of 18650 cells with a continuous discharge current higher than the ones featured in this review.
There are a couple of reasons for this. First, it's harder to provide a reliable current path. Second, capacity drops significantly, defeating the whole point.

For some reason, these batteries aren't available in the Vapcell store on AliExpress, and the link leads to a different product. You'll find out which one and why at the end of the review.

The packaging is familiar for Vapcell batteries: a black case with a clasp. Note that the ones at the link probably won't come with a case.



Specifications from the Vapcell website.
Model: INR18650 2000mah 38A
Size: 18.3*65.0mm
Typical Capacity: 2000mAh (0.2C discharge)
Min capacity: 1900mAh (0.2C discharge)
Nominal voltage: 3.60V
Max Continuous Discharge Current: 38A
End-of-charge voltage: 4.20V
End-of-discharge Voltage: 2.5V
Weight: 48g ( Appr)
Internal resistance: 8mΩ ( Appr)（AC 1kHz）
Standard Charge: 1000mA,CCCV 100mA cut-off
Quick Charge Current: 4000mA

They're wrapped in black heat-shrink tubing. Unlike most other Vapcell batteries, they don't have a numeric code indicating the type and capacity. The positive terminal is flat.


Dimensions and weight.


The batteries initially had about a 25% charge. After a "conditioning" cycle, they fell just short of the rated 2000mAh.


As is often the case, these batteries support two charging modes: standard at 1A and fast at 4A.
Charging at 1A took 2 hours. The CV phase was short, but the capacity measured during the charge cycle was also slightly below 2000mAh.


Charging at 4A took 36 minutes, which is pretty good, although that's a 2C current.

By the way, I've been asked several times about batteries that support a high charging current. These are a good example.


The Danish reviewer's website has a test graph for these batteries, which is also posted on the Vapcell page.


In my case, I tested them at slightly different settings: 0.2, 0.5, 1, and 2C, then 10, 15, 20, 30, and 38A—for a total of 9 tests.
Here too, the battery fell slightly short of its rated 2000mAh. The final capacity at 0.2C was 1985mAh, or 7.368Wh.


Temperature rise at 20, 30, and 38A. It's on the high side, but tolerable. I think the low capacity played a part: the battery simply didn't have time to overheat.


The second sample produced almost identical results.


The temperature was also very similar.


The graph comparing the cells' characteristics shows results at 0.2C, 1C, 10, 20, and 38A.
The results are close to ideal.


I also ran a "further discharge" test: the battery was discharged at 38A, then, after cooling down, discharged further at 0.2C to measure its remaining capacity. The battery delivered just 35 mAh, which is also excellent.


The batteries' impedance was around 7.7 mΩ. Here are the results after delivery, after "normalization," and at the end.


Now I'll get back to why the link in the title leads to a different battery.
During testing, I noticed the characteristic slope of the discharge curve, and given the stated specs, I started wondering: could these be Samsung INR18650-20S cells?
What pointed to that was the high stated discharge current, the 2000 mAh capacity, and the discharge curve. Also, I simply don't know of any other batteries with similar specs.

I'd already tested the Samsung INR18650-20S. The small difference in capacity can be attributed to measurement error, temperature, and the different ages of the cells.


The only thing that introduced some uncertainty was the maximum continuous current, which is specified as 30 A for the 20S.
In reality, it's a little more complicated: their maximum continuous current is 22 A. A current of 30 A is allowed if you accept a reduction in cycle life to 250 cycles. The datasheet says nothing about 38 A.


The temperature was also quite similar, at least at 20 A and 30 A. I couldn't test at higher currents back then.


The impedance is also very similar, and the batteries have the same positive terminal shape.


Conclusion.
I believe the batteries reviewed here are Samsung INR18650-20S cells in rewrapped packaging, and they're genuinely good cells.
That said, these batteries are noticeably outdated, but they're still hard to find an alternative to, especially if you need to build a battery pack with the best possible size-to-power ratio.

By chance, I ended up testing not only the batteries covered in this review, but also the Samsung INR18650-20S cells linked to in the title.
It would all be well and good if not for the price. On AliExpress, the 20S cells are listed at $8 each in a 2-cell lot and $7.37 each in an 8-cell lot. When I wrote my 20S review, they cost €2.95 on NKON, or about $3.50–3.60 including shipping, which was noticeably cheaper. Even now, they're €3.99, or about $5 including shipping, which is still less than $7.37.

While browsing the Vapcell store, I came across batteries with similar specs but a different appearance—link—and they're a little cheaper.

In short, these are good batteries with no quality issues, but they're seriously overpriced. That's all for today. I hope you found this useful.