Samsung INR21700-33J 3270mAh batteries: you won't find them cheaper

I was starting to think there wouldn't be any battery reviews for a while, but then one of my readers got in touch and offered to test some rather unusual and interesting cells from Samsung. Naturally, I agreed—especially since I was curious myself.

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Of course, the capacity is quite low for batteries in this format, and the discharge current isn't very high either, but the price is just €1.25 each! Yes, shipping costs extra, but out of curiosity I worked out how much 120 of these cells would cost with shipping. They fit exactly within the €150 limit, and the total came to €165, or about $180—roughly $1.51 per cell. I think that's a really great price for branded batteries.

I was sent two samples to test, and we'll put them through their paces :)


These batteries do have one fairly significant drawback: the positive terminal is aluminum, which immediately makes welding or soldering more difficult. The store does offer these batteries with copper tabs already welded on, though, in three configurations:
1. Positive terminal only - €1.45
2. Positive and negative terminals in a U configuration - €1.45
3. Positive and negative terminals in a Z configuration - €1.35.

I've always been puzzled by how Nkon sets its prices, and this is another example: for some reason, the version with one welded tab costs more than the one with two in a Z configuration...



I easily found a datasheet for these cells online, and it contained some interesting information explaining why the positive terminal is aluminum. Google translation:


Yes, these batteries were made for Tesla.

These batteries also have distinctive discharge characteristics. Whereas the lower cutoff is usually 2.5–2.75 V, here the discharge cutoff voltage is 3 V. There are also some differences in the charging profile, though they apply more to specific operating conditions. More on that later.
I've always liked how manufacturers label their batteries and list their specifications. Samsung hasn't let us down here, either. So:
1. The battery model number is 33, hinting at 3300mAh
2. The typical capacity is specified as 3270mAh
3. The capacity used in the specifications is 3200mAh


Operating and storage temperature ranges are given, with exposure duration specified as well—not just the temperature.


But the claimed cycle life is more interesting. I mentioned above that the charging profile differs. The standard specification calls for charging to 4.2 V, but there's a caveat—and it concerns cycle life. To get the claimed 2,000 cycles, you need to meet the following conditions:
1. Charge to 4.1 V at 0.5C, with cutoff at 0.05C
2. Discharge at no more than 0.5C
3. All of this at a temperature of up to 23°C.
4. They can also be used at temperatures up to 40 degrees, but their service life will drop to 1,500 cycles.

Something tells me that if you take any name-brand battery and use it under these same restrictions, it will last about as long.



The appearance is typical for batteries from this manufacturer. They have a unique matrix code, as well as markings under the heat-shrink sleeve, but this is the first time I’ve seen a solid positive terminal. I wonder how its vent valve would work—and if it does open, you can’t restore it afterward...

I may be wrong, but judging by the markings, they were manufactured in late April 2018. If I’m right, that explains the low price.



Dimensions and weight.


The batteries arrived fully charged and, judging by the writing on the casing, had even been measured already—but more on that later.
A run on a regular charger showed a capacity of about 3500 mAh.


The standard charging current for these batteries is 0.5C, but they can also be charged faster at 1C.
At 0.5C, a full charge took 2 hours and 36 minutes—not great, but acceptable considering these aren’t high-current batteries.


At 1C, charging took about 1 hour and 40 minutes, but I wouldn’t recommend using this mode. The optimal charging current is 1–2 A.


With a 21700 size and a capacity of 3200 mAh, you’d expect good current delivery, but the reality is much more modest. The manufacturer specifies a maximum of just 2C, or 6.4 A—quite low. It’s clear these batteries are intended for large packs, where the current per cell is reduced by using more cells.


The manufacturer lists the standard set of discharge rates: 0.2, 0.5, 1, and 2C. For my test, I decided to add 1.5C first, and after the first battery passed the 2C test successfully, I decided to try 3C as well.
The results are quite good: 3377 mAh at 0.2C is noticeably higher than both the rated 3200 and the typical 3270. But at 3C, it’s clear the battery can’t keep up. The actual sustained maximum is still 2C.


The temperature was also fine. I measured it at the end of the 1.5C, 2C, and 3C cycles. Since the temperature rise at 2C was small, I decided to extend the test to higher loads.


Since these are name-brand batteries, the results for the second one were entirely predictable.



A test comparing their characteristics showed everything was fine at 0.2C and excellent at 1C. But at 2C, the difference became more noticeable for some reason. That happens fairly often, though: the spread increases at maximum operating levels.


As an extra, I decided to run a couple more tests. First, charging at 0.2C—a mode listed for these batteries, which is quite unusual.


Yes, it takes a long time—more than five and a half hours—but what can you do? “Beauty requires sacrifice.” At least the manufacturer says that at this current, the battery reaches 100% charge.


To be honest, I was skeptical that charging at 0.2C would give us a 100% charge, while 0.5C would only give 95%. Sure, if you charge at a really high current, there can be some nuances, but at 0.2C versus 0.5C, the results should be about the same.
So I decided to compare them, and the difference turned out to be within the measurement error. Yes, the battery has "worn out" a little over the few cycles I ran above, but I think we can safely ignore that. Besides, the air temperature during the second test was a few degrees higher, which more than compensated for the slight "wear."

Blue shows the result after charging at 0.5C, red shows the result after charging at 0.2C.



As an extra, I ran one more test: after fully discharging the battery at 0.2C, I continued discharging it at the same current down to 2.5 V to see what we lose by stopping the discharge earlier.
Well, what can I say? 51 mAh. There really is no point in discharging these batteries below 3 V. Also, if you look at the graphs above, you can see that at 0.2C the discharge curve gets quite steep toward the end.


I measured the impedance when the batteries arrived and again at the very end. The results clearly show that these batteries aren't designed for high current.


I almost forgot. The batteries originally had some numbers printed on them, and they’re still there, in fact. The numbers look a lot like capacity measurement results. If that’s what they are, I have no issue with the relative values—they could certainly be the same. But I have bad news about the absolute values: they’re clearly much too high.



Conclusions.
Everything in life is a compromise, and these batteries are no exception. That’s why they have:
1. Low capacity for their relatively large size
2. Low current output

But on the other hand:
1. A very low price, especially per Wh.
2. A claimed cycle life of 1500–2000 cycles.

One other drawback is the aluminum positive terminal, and they were presumably manufactured quite a while ago.

Even so, I can say these are interesting batteries. If you don't need a good size-to-capacity ratio—for example, in portable devices—you get excellent value for money in terms of capacity. Another plus is that their actual capacity is even higher than claimed, and they’re genuine branded batteries.

That’s all from me. I hope this was useful, and thanks to Stanislav for providing the material for this new review :)