Another batch of batteries: Samsung ICR18650-26HM

Another batch of batteries has landed in my hands, this time Samsung ICR18650-26HM. These batteries are notable mainly for their price, since capacity and maximum discharge current clearly aren't their strong points. But why not test them, especially when I have the time and feel like it? I'll also try to clear up a couple of misconceptions about batteries.

I ordered quite a few batteries, and 24 of them ended up with me. I ordered three lots of 8, and they arrived in the usual cardboard packaging. In my opinion, this is the most convenient type of packaging, although some people prefer plastic cases. Lots in cardboard packaging are usually a little cheaper, so that's what I'd choose.



Judging by the THR1 marking, the batteries were made in 2017 (H), in April (R), during the first week (1). Fairly fresh.



The dimensions match the specifications exactly, but the weight is 3 grams below the stated value. To be fair, though, the spec says up to 47 grams, so we can say they match.



There's not much else to say, so logically I should move on to the tests. I will, but a little later. First, I'll tell you a bit about the Opus 3100 v2.2 chargers I ordered.
I ordered them from Gearbest too. There was a sale on, and I happened to spot it on my own blog. I bought a couple for friends, but they came to me first.


At first glance, the charger looks no different from the ones I bought on eBay before. If it weren't for one drawback—and a pretty serious one at that.


The thing is, it overheats. As far as I can tell, this is an updated version with a quiet fan, and that's exactly why it overheats.
At first, I didn't even understand what was going on. A while after starting the test, I looked at the display and saw 0, 0, 0, 0 mA instead of 1000, 1000, 1000, 1000 mA.
I tried restarting the test and even checked my big battery roundup to make sure I'd set the discharge current to 1000 mA there too.
It turned out that with a discharge current of 700 or 1000 mA and four lithium batteries, the charger overheats in discharge mode, shuts itself off, waits until it cools down, then turns back on and continues the test. It's nothing catastrophic, really; the test just takes noticeably longer, which is still inconvenient.


I tested the first batch of batteries “as is,” which is why the test is still in progress in the first photo—I had to restart it. The display shows a charging current of 500 mA; I later switched it to 700 mA.
According to the “Opus,” the batteries have a capacity of about 2800 mAh.


Since I really didn't want to wait around, I rigged up a fan to blow air over the charger, temporarily powering it from a handy battery.
Everything works great this way. Just to answer a question you might have: no, there won't be an “Opus” review.


The second batch—another 12 batteries.


But since I don't really trust this charger, I switched to a more familiar test using an electronic load.
First, here's what and how we'll be testing.

Let's open the datasheet for this battery model. We find that its nominal voltage is 3.6 V, not the usual 3.7 V, but the charge termination voltage is the familiar 4.2 V.
We can also see that the stated capacity of 2600 mAh is specified under the following conditions:
Discharge current: 0.2C, or 520 mA
Discharge cutoff voltage: 2.75 V
Standard charging current: 1300 mA (0.5C).


The stated capacity is achieved at a temperature of 25 degrees. That's no problem either: we turn on the air conditioner, cool the room to about that temperature, and move on to the tests.


To remind you what the screenshots will show, here's a quick reference.


For the test, I picked a pair of batteries almost at random. More precisely, I took the eighth and twelfth batteries from the first photo with the “Opus” chargers. The chargers measured their capacities as 2855 and 2831 mAh, respectively.
The first battery—and the first misconception I'll try to clear up:
Some users think that the difference between the capacity put in and the capacity taken out should be significant. To clarify, this is true of other types of batteries, such as lead-acid, nickel-cadmium, and nickel-metal hydride.
Lithium batteries are a little different: their discharged and charged capacities in mAh are almost the same. For example, the screenshot shows that the batteries delivered 2636 mAh, then took 2670 mAh to reach a full charge—a difference of about 1%.
But if you look more closely at the screenshot, you’ll also notice the capacity in Wh, which gives a more accurate picture of the batteries’ energy capacity. That’s where the catch is.
The battery delivered 9.651 Wh, then took 10.45 Wh to recharge—a difference of about 10–11%. That’s the battery’s “efficiency,” which in this case is about 90%.


The second battery showed practically the same specs: a capacity of 2635 mAh versus 2636 mAh for the first one, and the capacity in Wh was exactly the same at 9.651 Wh. Excellent consistency.


Since I saw a discharge option at a maximum current of 2C (5.2 A) in the datasheet, I decided to test that too.
According to the table below, the capacity should be at least 80% of the rated capacity measured at a discharge current of 0.2C (520 mA).


Well, the capacity in mAh actually turned out to be higher than at a discharge current of 0.2C, but the capacity in Wh dropped noticeably—by about 10%. That’s the price you pay for operating at high currents.



At the end of each test, I measured the battery temperature. It was around 60–62 degrees, with the highest temperature at the center of the case. The third photo is just an overall view of the “test setup.”


Now I’ll try to dispel a second misconception. I’ve been told several times that these batteries take a very long time to charge. More specifically, a full charge at 0.5C (for example) takes 3–4 hours. The datasheet even lists a charging time of 3 hours at this current.
No problem: set the charging current to 1300 mA, with cutoff when the voltage reaches 4.2 V and the charging current drops to 1/10 of the set value, or 130 mA.
After 2 hours, the battery had received almost its full capacity—about 2529 mAh—and the charging current had dropped to 600 mA.


Another 25 minutes later, the charger switched off. The battery had taken in another 127 mAh. So these batteries can be charged to 95% in two hours at 0.5C, then take in the remaining 5% over the next 25 minutes. That makes the total charging time 2 hours 25 minutes.


Mostly out of curiosity, I also checked the battery’s average voltage during discharge. This is the voltage you see on the battery label, for example 3.7 or 3.85 V. In this case, it was 3.66 V, compared with the rated 3.63 V.
This is more of a side note about what the voltage printed on a battery actually means.


That’s about it. I can say these batteries are good, fresh, and well worth buying.
In my opinion, they’re suitable for repairing laptop batteries, power banks, flashlights, and the like. But they’re not suitable for cordless drills or e-cigarettes.

Here’s a short video to round things off.