Vapcell K40 21700 4000mAh 30A/45A batteries

Another set of high-current 21700 batteries, with a capacity of 4000mAh. This is already my fourth review of batteries with similar specs, so I have plenty to compare them with—and I’ll do that at the end of the review.


I’ll try to keep things as brief as possible today.
The batteries come with a two-slot case, as do most Vapcell batteries.



Specifications from the Vapcell website.
Model: K40
Size: 21.1*70.6mm
Typical Capacity: 4000mAh (0.2C discharge)
Min capacity: 3900mAh (0.2C discharge)
Nominal voltage: 3.60V
Max Continuous Discharge Current:30A
Max Discharge Current: 45A with 80℃ cut
End-of-charge voltage: 4.20V
End-of-discharge Voltage: 2.5V
Weight: 68g ( Appr)
Internal resistance: 10mΩ ( Appr) （AC 1kHz）
Standard Charge: 2000mA,CCCV 100mA cut-off
Quick Charge Current: 6000mA

They’re brown, and the design is no different from that of the other batteries sold by this company.
The positive terminal is flat and has a three-beam design.


Dimensions and weight.


They arrived charged to about 25%. In the “conditioning” cycle, they delivered slightly more than the rated 4000mAh.


Two charging modes are specified: standard 2A (0.5C) and fast 6A.
In standard mode, a full charge took 2 hours and 8 minutes, which is very good.


In fast mode, the battery charged in 50 minutes, which is also good.
Based on the test results, I’d probably recommend a charging current of 4A as a reasonable compromise between speed and wear.


Vapcell’s website has a test graph for currents of 2, 10, 20, 25, 30, and 35A.


But, as always, we’ll “go our own way,” so I’ll run a few more tests: 0.2, 0.5, 1, 2, 3, 4, 5C, and 30A. The main difference from Vapcell’s tests is that I didn’t test at 35A.
The results already show a uniform voltage drop as the load current increases, which means the battery isn’t being “overloaded.” Capacity at 0.2C was 4.049mAh, or 14.71Wh.


Temperature was also fine: even at 30A, the battery only heated up to 90 degrees.
Below are the results at 16, 20, and 30A.

It’s interesting how the thermal camera “sees” the battery’s markings.


The second sample was practically identical in every respect.




After it cooled down, I discharged it further at 0.2C and got 114mAh—pretty good.


Comparison of how closely the two samples match at 0.2, 1, and 5C, and 30A.
The second sample falls behind very slightly, but overall the match is excellent.


Battery impedance on arrival, after “conditioning,” and at the end.


As a small extra, here’s a screenshot from another review showing the number of puffs from an e-cigarette.


And, of course, a comparison with other batteries.
Vapcell has a graph comparing these batteries with Samsung and Molicel at 30A.


Unfortunately, when I tested high-current batteries before, I could only plot graphs up to 20A, so the comparison graph shows results at 1C and 20A.
On the other hand, my comparison includes not only the models listed above, but also the Basen BS217A. I really regret not plotting the Litokala 21700 4000mAh back when I had the chance.

Overall, they look good, but if you look closely, I think you’ll notice that the graph for the batteries under review is identical to the graph for the Samsung INR21700-40T.
I think it's clear even without a microscope that these are the batteries in question. If you have doubts, follow the link above and compare them.
The only strange thing is why Vapcell rates them for a maximum current of 30 A, when, as I recall, the Samsung 40T can handle up to 35 A continuously without temperature monitoring, and up to 45 A with it.


Conclusions.
These are essentially Samsung INR21700-40T cells in different packaging, so I can only say good things about their specs, both in terms of current output and how closely they match the stated specifications.
My only complaint, as usual, is the price. Unfortunately, I can't do anything about that.

That's all from me. I hope this was useful, and as always, I'd be glad to hear your comments.