BAK N21700CG 5000mAh Batteries from Nkon

This will be my last battery review for a while. I don't know when the next one will be, and today we're looking at BAK 21700 batteries.

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I realized today that I don't have any batteries left to test. I have no idea when I'll get more, but if you have any suggestions, I'd be happy to consider them.

As for the cells in this review, they were also bought for power banks, in a batch of 65 (16 × 4 + 1 spare). In the end, I haven't used them yet, although, as with all the previous ones, I've fully tested them and measured the capacity of every cell.


According to the datasheet, the batteries have a nominal capacity of 5000 mAh.


What I didn't like was the completely unclear labeling. I only found out the name from the product page, so, for example, I wouldn't be able to prove that these are actually the batteries named in the title.



The Vapcell charger showed a capacity of about 5000 mAh. By the way, I've noticed that the first channel consistently reads lower than the fourth. I don't think I noticed this before, though it would be more accurate to say that the fourth channel has started overreading.


The datasheet says the standard charging current is 0.5C, but if you're in a hurry, charging at 1C is allowed.
At 0.5C, charging takes a little over two and a half hours, which is normal for high-capacity cells. Still, I'd prefer a shorter CV phase.


At 1C, charging takes about an hour and a half. I can say that 1C is a very high current for these cells; I wouldn't recommend charging them at more than 2 A at all.


The maximum discharge current is 3C, or 15 A. Interestingly, Nkon's product page lists 10.2 A. I don't know where they got that figure; the datasheet specifies 3C.
The datasheet includes a capacity-versus-load-current graph, with clearly specified rates of 0.2, 0.5, 1, 2, and 3C—not just some arbitrary current. I added another test rate, 1.5C. In all cases, C = 5000 mA.

I didn't quite get 5000 mAh, although the batteries are within the stated range. I'd also say that 15 A is a bit much for these cells: you can see how much the voltage sags at that current. Their realistic operating current is 1–2C.


The temperature results, on the other hand, look good. Below are the results at 7.5, 10, and 15 A. In my opinion, around 72 degrees at the maximum current is quite good.


The second cell gave similar results for both capacity and temperature.



Speaking of temperature, the datasheet has a graph showing how available capacity varies with temperature. It shows that the manufacturer expects these cells to be used at -20 as well. It's also interesting that capacity drops at higher temperatures, although my own observations suggest the opposite.


The cells are also consistent in their characteristics. There's a small variation, but in my opinion it's well within the measurement error.


The batteries have an impedance of about 13.5 mΩ, which is typical for cells like these.


There are so many batteries in this comparison that it makes me a little nervous, and unfortunately the graph is becoming less informative. I don't know how to compare batteries going forward in a way that's both clear and able to include a lot of them. The only thing I can do for now is split the comparison into three stages: 0.2C, 1C, and maximum current (3C).
The comparison includes:
1. The batteries under review (red)
2. LG INR21700-M50LT (orange) - review
3. LG INR21700-M50T (yellow) - review
4. Samsung INR21700-50E (green) - review
5. Samsung INR21700-50G (cyan) - review
6. Vapcell 21700 T50 (blue) - review
7. Vapcell F52 21700 (purple) - review
8. Vapcell G50 21700 (pink) - review
9. INR21700M52V (brown)- review
10. Vapcell P50 21700 (black) - review

At a 0.2C current, the results are average.


At 1C, practically nothing changed; it's still an average performer.


As before, at a 3C current, three groups stood out: a couple of cells lagged far behind, one pulled ahead, and the rest hovered somewhere in the middle—which is also where the cells under review landed.


Conclusions.
As with the LG INR21700-M50LT, this is a solid mid-range performer. It clearly doesn't lag behind, but it doesn't shine in capacity (models rated at 5600–5800 mAh are more competitive here) or current output (that's where the Samsung INR21700-50S rules). Overall, these are good batteries for flashlights, power banks, and similar devices—in other words, applications that need high capacity under a light load at a reasonable price.

I also have all the data for these batteries in Ah and Wh for each cycle: first discharge, full charge, full discharge. I haven't compiled it into a table, though all the cells are labeled. In today's review, these were cells 64 and 65. I'm not even sure whether I'll put the data in a table.

That's all for today. I hope you found it useful. Thanks for reading.