LG INR21700-M50LT Batteries from Nkon

Yes, batteries again, but this time from the popular Nkon store. In my opinion, these are the best batteries so far in terms of price and specs.

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This review comes with a small bonus, but otherwise it's simply a review of some good batteries.

I bought a lot of them. Some went into power banks, and I still have some left; the photo shows far from all of them.


They look very similar to other battery models from this manufacturer.


Interestingly, the datasheet doesn't specify the capacity in mAh, only in Wh. However, judging by the charging and discharging parameters, the capacity is 4800 mAh—that's the value the specs are based on.
Interestingly, Nkon lists the following specs:




The markings and matrix code make it clear that these are genuine batteries. The production date is January 12, 2022.


Dimensions. By the way, when I was figuring out how to make a compact power bank, this was the biggest headache: the batteries fit with virtually no clearance. I didn't think even 0.1 mm could make a difference.


It's useful that the datasheet shows not only the dimensions, but also what the batteries look like.


Capacity is about 4900 mAh. This isn't a "normalization" cycle; that had already been done when the batteries' capacity was measured in preparation for assembling them into packs.


According to the datasheet, there are two charging modes: standard, at 0.3C (1.44 A), and fast, at 0.7C (3.36 A).
In standard mode, the batteries take a charge really well, although the process is, of course, very slow overall.


At 0.7C, though, the CV phase takes a very long time, so I wouldn't recommend charging them at more than 1.5–2 A. You won't speed things up much, and you'll shorten the battery's life.


The maximum discharge current at an ambient temperature of 10–25 degrees is 3C, or 14.4 A.


Testing was done at 0.2, 0.5, 1, 1.5, 2, and 3C, where C = 4.8 A.
The battery fell just short of 4900 mAh, but comfortably exceeded its rated 4800 mAh. The rated capacity in Wh was listed as 18.2 Wh; I measured 18.1 Wh.
And this is where things get a little confusing. Based on the charge/discharge rates specified in the datasheet in terms of C, these cells have a capacity of 4800 mAh. I measured almost 4900, but the rated capacity in Wh is 18.2, and I measured 18.1. It all falls within the stated specifications, of course, but it's a little puzzling.


As the model name suggests, these batteries are an extension of the M50T line, possibly an improved version. But I can already say that there are major improvements in terms of temperature. The M50T reached 54, 63.7, and 89.7 degrees at 1.5, 2, and 3C, respectively; these reached 47, 56.8, and 71.3 degrees. In my opinion, that's a pretty significant difference.


The second sample is essentially the same.



One important reason I chose genuine batteries was the consistency of their specifications. I mention this very often in my reviews; sometimes it can matter even more than maximum capacity.


It's also interesting that the specified impedance is 15 mΩ ±6 mΩ! That means it could range from 9 to 21 mΩ, although I have to say, I don't remember ever seeing a spread of 1 mΩ.


The impedance here is about 14 mΩ. Excellent.


Naturally, I wanted to compare them with other batteries:
1. The ones under review (red)
2. LG INR21700-M50T (orange) - review
3. Samsung INR21700-50E (yellow) - review
4. Samsung INR21700-50G (green) - review
5. Vapcell 21700 T50 (light blue) - review
6. Vapcell F52 21700 (blue) - review
7. Vapcell G50 21700 (purple) - review
8. INR21700M52V (pink) - review
9. Vapcell P50 21700 (black) - review

At a 0.2C discharge rate, the batteries under review lag behind all the others in capacity in mAh, but are around average in energy output in Wh—and under certain conditions, that can matter even more.


At 1C, the picture is practically identical


At the maximum current, things change a little: some clear laggards emerge, for whom this current is too high and whose voltage sags significantly. But one battery clearly holds a higher voltage under these conditions: the Vapcell T50, which is based on Samsung's 50S cell.
Otherwise, the picture remains unchanged: the M50LT lags in mAh output, but sits somewhere in the middle in Wh output.


But I was much more interested in comparing it with its predecessor, the M50T. And here I can say unequivocally that the M50LT tore the old-timer to shreds. The new model is much more efficient, although the M50T did try to put up a fight at a low discharge current.


That could have been the end of the review, but I can't resist sharing some more interesting information: statistics from a relatively large number of batteries.
When I started building power banks, one of my main ideas was to use not only high-quality cells, but also cells matched into packs. But is that really necessary? I often hear people say, “What's the point? The variation is small, and on average everything will even out anyway.”
But no—my inner perfectionist woke up, and I wanted to do it right. As they say, “Do it as well as you can; doing it badly will happen on its own.” Of course, I had to test the idea first.

In the end, I tested all the batteries—almost 500 of them, although some weren't LG cells. For this, I used an eight-channel battery tester and put together a simple program that ran a discharge-charge-discharge-charge cycle, with the final cycle charging the battery to about 20%.
Each battery was labeled and assigned its own number. In a day, I could test four batches of 8, or 32 cells—just enough for two battery packs.


The result was a complete graph of the test cycle. I also saved the test results for each battery, just in case.


The battery tester can also generate a summary table at the end of a run, but it wasn't very useful to me because it doesn't include results in watt-hours.


Next, I combined all the data into one table. Here I've grouped the test results for 240 cells at a 0.5C discharge rate. In practice, I found that the spread in a batch like this can be as much as 100 mAh. I wouldn't call that a lot, but it's worth remembering that these batteries all came from the same production batch.


Today, just out of curiosity, I made a histogram showing that most of the capacities fall in the 4760–4800 mAh range.


To get a high-quality battery pack that I could be 99.9% confident in, I entered the test data for 240 cells into a calculator and created 60 groups of four cells in parallel. The mathematical spread in each group was 1 mAh—or, more accurately, ±0.5 mAh, since the difference from the ideal was either 0 or -1, and there wasn't a single case of +1.


After that, I had a large table that I used to assemble the 4P groups. I had the cell numbers both in the table and on the cells themselves.
Each battery consists of four parallel groups, i.e. a 4P4S configuration. Since every 4P group was practically identical to every other one, I could assemble everything like a construction set, and the right battery pack would come together “automatically.” What's more, I could just as easily build any battery pack—4P9S or even 4P14S—and still end up with a properly matched combination.
Besides reducing imbalance, this also gave me the maximum possible battery capacity: 19.138 Ah. At 3.6 V, that's 275 Wh at a 0.5C discharge rate; at the standard 0.2C rate, it would be 285–290 Wh. I state the battery capacity as 285 Wh—that's more honest, especially since it corresponds to a five-hour discharge at a load of around 60 W.



The batteries were also tested to identify any possible defects, and I did find one faulty cell. It was a Samsung 50E; the graph shows the voltage fluctuating, so I suspect a poor connection inside the cell. If a battery like that had ended up in a pack, it would have caused a serious problem... Good thing I always bought at least one as a spare.


Conclusions.
I won't claim these batteries are top-tier in terms of capacity or discharge current—there are better ones, as you can see in the comparison table. Their advantage is the great balance of price and performance; in my opinion, it's just right. They're also genuine, new batteries, which means a long service life.

I'm not sure whether I'll review the power bank; I'm still thinking about it. I do have a few more of them, though, as well as some tested batteries that could also be used to build proper custom battery packs. Get in touch if you're interested.

That's all for now. Thanks for reading. I haven't decided what to cover in my next review yet. I recently got another batch of assorted used transistors, so maybe I'll test them and post the results.