Review and test of batteries from nkon.nl: Samsung INR18650-35E

This is the second pair of Samsung batteries from the NKON store. Today we'll be looking at so-called high-capacity batteries, designed to prioritize capacity over discharge current and internal resistance.


As you may have guessed, these are Samsung INR18650-35E batteries. In my opinion, Samsung is being a little misleading here: judging by the name—or, more precisely, the last two digits—you might think these batteries have a capacity of 3500 mAh.
In fact, the rated capacity is 3400 mAh, and all the test conditions are based on that figure. For example, 0.5C is listed as 1700 mA, and 0.2C as 680 mA. Honestly, that seems a bit misleading to me. They might as well have called them the 34E.



But back to the batteries themselves. They look very much like the previous 30Q cells; as they say, the differences are in the details.
The date of manufacture is marked on the heat-shrink sleeve as IG1T.

Samsung batteries generally use two types of markings: one on the heat-shrink sleeve and one underneath it.

On the heat-shrink sleeve:
The first digit indicates the Samsung facility where the battery was manufactured.
The second letter indicates the year of manufacture: Q - 2008, S - 2009, Z - 2010, B - 2011, C - 2012, D - 2013, E - 2014, F - 2015, G - 2016, H - 2017, and so on.
The third letter or digit indicates the month of manufacture: 1 - January, 2 - February, 3 - March, 4 - April.... A - October, B - November, C - December
The fourth digit indicates the week of manufacture, from the 1st to the 5th.

Under the heat-shrink sleeve:
1 — production line number
2 — model number
3 — year of manufacture: Q-2008, S-2009, Z-2010, B-2011, C-2012, D-2013, E-2014, F-2015, G-2016, H-2017, and so on…
4 — month of manufacture: 1-January, 2-February, 3-March, — A – October, B – November, C – December

Everything would be fine, except that the first marking suggests January 2016. But the T at the end doesn't look anything like a week code, and it doesn't work when I try to identify it using the online helper either; it returns an error when I enter the last letter.
Also, the first character in this type of marking should be a digit, not a letter.

There are also markings under the heat-shrink sleeve:
E5IG
B3031

The first one looks like a date code, but according to information I've found indirectly, Samsung uses K for 2018, not I, as would make sense. Even if it does indicate 2018, the last character still can't be G, since the month codes run from A to C, and the last character definitely isn't 6 or C.

I won't draw any conclusions for now. I couldn't determine the date of manufacture; all the sources I found repeat the same information. I can only guess that it was made in January 2016.


The dimensions are as specified, and the weight listed in the datasheet is up to 50 grams, which checks out too.


The specified internal resistance is no more than 35 mΩ.


Both batteries have an internal resistance of 20 mΩ.


The batteries were initially charged unevenly, to around 30–40%. Charging them and then discharging them gave an estimated capacity of 3550–3590 mAh.


Things get more interesting from here. Before testing with a more accurate device, I checked the datasheet again and found capacity figures for different discharge currents. But there was a modest footnote at the bottom:
Capacity as a percentage of the capacity at the standard discharge rate (assumed to be 0.2C) — 3350 mAh. So not even 3400, let alone 3500.


All right, let's get a proper holder and the EBC-A10H electronic load and start testing.


The battery charger was set to a 0.5C current (1.7 A), a termination voltage of 4.2 V, and a cutoff current of 70 mA (the datasheet recommends 68 mA).
Discharge down to 2.65 V, again as specified in the datasheet.

First battery, according to the graph:
Red — 0.2C — 680 mA
Orange — 0.5C — 1.7 A
Yellow — 1C — 3.4 A
Green — 6.8 A
Light blue — 8 A
Blue — 10 A



Battery temperature at discharge currents of
6.8 A, 8 A, and 10 A. The datasheet specifies a maximum continuous current of 8 A. Testing it at 10 A was my idea, since the battery performed quite well at 8 A.


The test on the second battery is a little shorter; it wasn't tested under a 10 A load.
Red — 0.2C — 680 mA
Orange — 0.5C — 1.7 A
Yellow — 1C — 3.4 A
Green — 6.8 A
Blue — 8 A


Temperature rise at 6.8 A and 8 A, respectively.


The capacity measurements match the stated 3400 mAh, so there are no issues there. The battery also performs very well under loads of up to 10 A, but for reliability, I wouldn't exceed the specified 8 A—which, incidentally, is higher than the 6.8 A specified for its closest competitor, the Panasonic NCR18650B.

But I personally have questions about the manufacturing date; I still haven't been able to determine it.