Decent budget BAK N18650CK 3000mAh batteries - 6.1A

Batteries made by BAK have appeared at the well-known Nkon store, and I’ve been asked several times to review batteries from this manufacturer.
As it happens, I have a few of them on hand.


To be fair, this company’s batteries have been around for quite a while, but Nkon has started offering them more actively only recently. I think this is due to some shortages and price increases for batteries from better-known manufacturers.
My friend decided to buy a few as part of the general trend, and since there isn’t much information about them, he gave me four to test.



These batteries have a datasheet, conveniently provided in both Chinese and English.

Also, if you noticed, the datasheet lists the batteries’ capacity as 3050 mAh, not 3000 as stated on the store page.


These are clearly industrial-grade batteries, with just the model name and a barcode with a serial number.


The code is unique to each battery. Judging by it, I’d guess they were made in 2019, possibly in week 22.


Dimensions and weight are standard for an 18650.


The initial charge was about 30%. In the “normalization” cycle, I got slightly more than the rated capacity; the discharge current was 1 A.


There was a little confusion about the charging parameters, but the explanation in the text of the datasheet cleared things up. It’s all straightforward: standard charging at 1.525 A up to 4.2 V, with charging terminated when the current drops below 0.01C, or 31 mA.
The maximum charging current is 1C, or 3.05 A.


The lowest charge cutoff threshold on my charger is only 50 mA, but I don’t think that’s critical.
A full charge at 0.5C took 2 hours and 38 minutes, which seems like a lot to me.


Increasing the charging current to 1C didn’t speed things up much: it took 1 hour and 47 minutes. I don’t think there’s any point in going above 0.5C with these batteries—the charge won’t be much faster, but wear will increase.


The batteries are rated for discharge currents up to 6.1 A, but since they performed quite well, I expanded the test, first to 2.5C and then to 3C. In total, I ran six cycles at 0.2, 0.5, 1, 2, 2.5 and 3C.

At the standard 0.2C, I got 3070 mAh, or 11.24 Wh—not bad.


Battery temperature at currents of 2, 2.5 and 3C.
At 3C, of course, you can feel the heat, but at 2.5C the battery only gets moderately warm.


The results from the second sample are a little better still.


Its temperature is also a couple of degrees lower.


The results at 0.2, 1, 2 and 3C are consistent, and both batteries exceed the rated 3050 mAh.


But my experiments didn’t go unnoticed by the batteries—their internal resistance increased noticeably.
Results after receipt, after “normalization,” and the final results. I should also note that the voltage at the battery terminals drops fairly quickly to 4.17–4.18 V after charging is complete.


But as you may have noticed, there were four batteries. My friend decided to improve the accuracy of the test by checking how much the results varied across a larger number of cells.

No problem—we run the same “normalization” cycle and get roughly the same results.


There were fewer cycles here. I ran the main ones: the standard 0.2C and the working rates of 1C and 2C.
Overall, everything is pretty much the same as with the previous pair.


I measured the temperature only at 2C, and it was all the same.


Since there were fewer cycles—and, more importantly, no overload or overheating cycles—the difference here is within the measurement error: on the left, after “normalization”; on the right, after three cycles.


And now the main question: how consistent are the results across four cells?
I plotted two operating modes and got a spread of 3070 to 3110 mAh at 0.2C, and 2937 to 2972 mAh at 2C.
So the difference is just over one percent, which is normal even for branded batteries.


Conclusions.
I’d call these very good batteries if it weren’t for one thing: I didn’t like how the impedance increased after they warmed up—about 10% above the original value. Yes, they were noticeably overheated, and I exceeded the current limit by 25% at first and then by 50%, but there were only two tests at those settings.
I don’t think the manufacturer limited the maximum current to just 2C for no reason—that’s low even for high-capacity batteries. The datasheet also specifies the maximum current depending on temperature.

Of course, you’ll ask what the point of these batteries is and where they should be used. It’s simple: the advantage is the price, and they’re well suited to laptop battery packs or other low-power devices. They also have consistent parameters, which makes them suitable for assembling battery packs.

There’s another possible use, though. For some reason, I have a feeling that manufacturers like Litokala and Varicore use something similar in their repackaged batteries. Why not? They can handle 10 A, and who cares if their lifespan is shortened?

That’s all for today. I hope you found it useful.