Testing INR18650-25R batteries from Ali after 3 years

Some time ago, one of my readers asked me for advice and also offered to send me some INR18650-25R batteries for testing. He had bought them on AliExpress several years earlier. The test was done simply “out of curiosity” and wasn’t intended to serve any practical purpose, but I did find a few interesting things.


The link in the title goes to a store that is very likely to sell genuine products, strange as that may seem for AliExpress.
The reader said he bought the batteries in early 2017, so they’re now more than 3 years old, but they haven’t been used at all. I’ll compare them with definitely genuine Samsung INR18650-25R batteries bought from Nkon, which I reviewed earlier.


They shipped from Russia and, surprisingly, arrived very quickly. I’d expected the whole process to take much longer.


They look just like the well-known and very popular INR18650-25R batteries.


The markings indicate that the batteries were made in late October 2016. There’s no matrix code; I don’t think they were using one back then.
At least externally, the batteries match genuine INR18650-25R cells.


Their dimensions are identical too, but they weigh about 1.5 grams more than the ones I bought from Nkon not long ago. I don’t think that difference is significant.


The batteries were almost fully charged to begin with. When discharged, they delivered almost the same capacity as each other, but noticeably less than the cells I tested almost a year ago. Those came in at around 2700 mAh; these are at 2500 mAh.


The full charging time was almost the same: 2 hours 12 minutes, compared with 2 hours 9 minutes for the previous cells.


Unfortunately, I accidentally forgot to save the test data at 0.2C for the first battery, so I only have a screenshot. There’s no point in testing it again now.


Test results at 0.5C, 1C and 2C, and at 10, 15 and 20 A. The sharp voltage sag above 10 A is immediately apparent, but I’ll come back to that.


At discharge currents of 10, 15 and 20 A, the temperature was about 5–6 degrees higher than for the cells I bought from Nkon.


The second cell produced almost the same results.



A check of how closely their characteristics match showed that things aren’t quite so straightforward after all. There is a difference, as the comparison at 0.5C, 10 A and 20 A shows.


The batteries’ impedance when received, after the preliminary test and at the end. There’s a fairly substantial difference compared with the previous cells: those had about 3–4 mΩ less impedance, which is quite significant.


Now the obvious question is: what kind of batteries are these? Judging by their appearance, they’re genuine: the look, color and shape of the positive terminal all match. Even the markings under the heat-shrink wrap differ between the two cells. And unlike Litokala, Varicore and others, the markings didn’t come off when heated, which also points to them being genuine.


But the test results tell a very different story. Below is a comparison of the cells under review (blue) and definitely genuine ones (red) at 0.2C, 10 A and 20 A. The difference is apparent not only in capacity but also in the discharge curve, which differs even at 0.2C, let alone at 10 and 20 A.


There are really only three possibilities here:
1. They’re counterfeit—in other words, they’re not Samsung cells at all.
2. They’re old, and their performance has deteriorated significantly over the past three and a half years.
3. They are Samsung cells, but not 25R.

I can rule out the first possibility: they look far too much like the genuine article. The second is also questionable. Performance does decline, of course, but it’s unlikely to decline this much. The third possibility is more plausible, but in that case their capacity at low discharge currents should be around 2.5 Ah. I can’t remember Samsung making cells rated at, say, 2.3–2.4 Ah.

At the moment, I’m leaning toward the second possibility, but I’m not 100% sure. Ideally, I should have tested them right away; time is an important factor and shouldn’t be ignored.

That’s all. I hope you found this interesting. Maybe you have your own thoughts on whether these batteries are genuine.