Another batch of Samsung batteries, this time protected ICR18650-32A cells (updated review)

Last month I posted a report about buying INR18650 — 25R batteries.
Today, here’s a report on my second “test purchase” from a store everyone knows. This time, though, the batteries are different: protected ICR18650 — 32A cells.

The batteries were ordered on November 9, shipped on November 17, and received on December 16 and 22.
No, they didn’t fall apart in the mail and arrive at different times for that reason. I simply ordered 40 at once, and they were shipped in two packages again.
The total cost of the order, including insurance, was $178.86.

In my previous review, I complained about the very poor packaging. This time, everything was noticeably neater. But I should point out that I received only half the order; the other half went to a friend. A couple of his batteries had minor damage, although they were fully functional.


This time, the batteries inside were packed in resealable bags, grouped in fours as ordered.


But three of the five bags looked roughly like this. The flimsy plastic couldn’t withstand the postal service’s rough handling and tore. A couple of batteries were trying to escape from one bag; the batteries in the others stayed put.


And here are all the batteries I received together. You’re not seeing things: there are 22 batteries in the photo, but the store didn’t throw in extras as a reward for my good review last time.
I just borrowed two batteries from a friend who received his a week earlier, even though they were shipped together.


As I mentioned above, these are protected Samsung ICR18650 — 32A batteries.
Manufactured in 2014, 18650 size, rated capacity 3200 mAh.


The positive terminal has three holes, though I don’t think that tells us anything.
The thing is, major manufacturers hardly ever make protected batteries. Protection is added afterward, so the “button” can be different.
In addition to the original heat-shrink wrap, there’s an extra transparent layer.
A strip runs along the entire side of the cell to the protection board.
The protection board is on the negative-terminal end.
No complaints about the appearance: the board is installed very neatly, and there’s a protective plastic holder.


I found the official datasheet for these batteries.
Here are a few of the specifications.


The datasheet stated that each battery weighs no more than 50 grams. When I weighed them, I got 51.8, but since these batteries have protection circuits, they’re bound to weigh more.
The protection board and plastic holder weigh about 1.6 grams, plus the heat-shrink tubing, which brings it to exactly 50 grams.


Then I moved on to testing and immediately ran into a snag.
The thing is, these batteries are long. To save time during testing, I give the batteries a “pre-charge” while another batch is being tested.
But these batteries only fit into a fairly decent branded charger sideways. And even then, only after a good shove.
The battery is 69 mm long and 18.5 mm in diameter.


They fit into the no-name charger without any trouble, though. Honestly, I thought it would be the other way around.
First, I ran some preliminary tests to check how repeatable the measurements were and get a rough idea of the capacity.
It’s only a rough estimate because the batteries have a charge termination voltage of 4.35 V, while the charger only charges them to 4.2


The numbering above isn’t a mistake. We just happened to accidentally kill one of the batteries. It doesn’t matter how, but it wouldn’t work, so I decided to take it apart.
I carefully cut away the clear heat-shrink tubing and got to the positive terminal.
The positive terminal is spot-welded via a small tab. This arrangement isn’t suitable for high currents, but I don’t think it’ll cause any problems at 3–4 A.


The protection board is on the negative terminal. I don’t know what the marking NXW-polar means; I was more interested in which components were installed.
The board has two 8205A MOSFET arrays (not to be confused with the S-8205A controller). Each MOSFET in an array has an on-resistance of 25–40 mΩ, depending on the supply voltage. Since the MOSFETs in each array are connected in series, while the arrays themselves are connected in parallel, the total switch resistance is also 25–40 mΩ. For calculations, we can use an average of 37 mΩ.
One array can handle a maximum continuous current of 5 A, so two can handle 10 A. But I wouldn’t use these batteries at currents above 3–4 A; it’ll be clear why below.
The controller is a DW01, a lithium battery protection IC.
According to the datasheet, it operates over a range of 2.4–4.28 V, which is a little odd in itself, since the batteries’ maximum voltage is 4.35 V. Perhaps a separate version of the controller is used.


After removing the protection board, the battery worked normally.


After sorting out the damaged battery, I moved on to the tests.


The number of batteries wasn't divisible by four, so there were only two in the last batch.
One of them was the “repaired” battery, which showed a capacity of 2976 mAh, although it had only been charged to 4.2 V.


For more accurate test results, I decided to test the battery without protection.
As I mentioned above, these batteries are originally sold unprotected, and the datasheet is for that version as well.
I'll also try to run the measurements as close to the datasheet conditions as possible.
First, I charged the battery to the manufacturer's specified 4.35 V. Charging was done at 1 A until the charging current dropped to 0.1 A, or 1/10 of the charging current.
Then I connected it to the electronic load, set the discharge current to 6.4 A (the maximum specified by the manufacturer), and reset the capacity counter.


The manufacturer specifies a maximum case temperature rise of 25 degrees above ambient.
The temperature was around 30 degrees at the start of the test, but the battery began to heat up quite a bit as the test went on.
Since I wasn't trying to overheat the battery, I first reduced the load current by 10%, but the temperature kept rising, so I had to reduce the current by another 10%.
I didn't reduce the current any further; I decided that was enough.


I ended the test at a discharge current of 5.1 A, which is 80% of the maximum specified by the manufacturer.
The capacity was 3023 mAh, and the battery heated up to 71.5 degrees.
Let's just say the result was disappointing.
In my opinion, that temperature is too high even at less than the full current.


Well, I thought, and decided to check the capacity at a current of 0.2C, since that's the current at which the manufacturer specifies a nominal capacity of 3200 mAh and a minimum capacity of 3100 mAh.
The battery showed 3094 mAh, quite close to the specified minimum of 3100 mAh.


In principle, I could have ended the tests here, but I was already getting into it and, just out of curiosity, ran a test on the new electronic load with a battery-testing function.
I set the charging current to 1600 mA (as specified in the datasheet), the voltage to 4.35 V, and the charge cutoff current to 160 mA. The discharge current was set to 1C, i.e. 3200 mA, and I started the test.

The test measured a capacity of 2923 mAh. That’s 100 mAh different from the previous test at 5.1 A. I’ll look into why later.
This also gives us a clear answer to the question of why the number of mAh “drawn” from a battery often roughly matches, and sometimes even exceeds, the number of mAh “put in.”
That’s because, in addition to capacity in mAh, there’s also capacity measured in watt-hours.
As you can see in the screenshot (click to enlarge), charging used 12.42 Wh, while we got 10.35 Wh back, so everything checks out: the battery’s efficiency is about 80%.


While I was at it, I also measured the battery’s internal resistance at currents of 1 A and 10 A.
The manufacturer specifies an internal resistance of no more than 100 mΩ.




And now for the conclusions.
The results are mixed. On the one hand, the capacity is almost as specified, and the internal resistance is even lower. On the other hand, the battery gets very hot at discharge currents of 2C.

Important update.
I retested the battery with its protection circuit, setting the discharge cutoff voltage to 4.35 V.
The current was set to 1.6 A. The battery was almost fully charged, and automatic cutoff was set to 0.16 A.
In fact, automatic cutoff occurred at 800 mA, which means charging was stopped by the protection circuit, not the charger. So it’s best not to set the charge termination voltage above 4.3 V, especially if you use smart chargers like the iMAX, which can raise the voltage above 20 V in this situation and damage the protection circuit.
Here’s the charging graph up to 4.35 V.


Here’s the graph for the full test: charging at 1.6 A, discharging at 3.2 A, then charging again at 1.6 A.
The protection circuit stopped charging at a current of about 500 mA.


During the experiments, I accidentally applied a 10 A load to the protected battery. The protection circuit cut off the load, and further tests showed that it disconnects the battery when the load current exceeds 5 A.

Pros
Protection circuit included
The protection circuit has two MOSFET assemblies, rated for a combined current of up to 10 A.
Capacity is close to the specified value and even exceeds it at a discharge current of about 2C (see datasheet).
Internal resistance is lower than specified.
Neat construction.

Cons
The protection circuit cannot operate for long at 4.35 V, cutting off battery charging prematurely. This reduces the battery’s performance but extends its life.
The battery overheats at a discharge current of about 1.5–2C.
The protection circuit makes the battery very long: 69 mm instead of 65 mm.
At a discharge current of 0.2C, capacity still fell slightly short of the specified minimum of 3100 mAh. Perhaps that’s because these batteries were made in 2014.

I don’t know if this review will be useful, but I tried to include as much information as possible. If anything’s missing, let me know and I’ll add it.