Review and test of batteries from nkon.nl, Sony/Murata VTC5A

Another pair of interesting batteries from nkon, and this time they’re Murata VTC5A cells. They don’t have particularly high capacity, but they can deliver a lot of current.
Review, tests, and a few oddities.


I think many people know these batteries better as Sony VTC5A, but they’re now made under the brand of another major company, Murata. Since essentially only the name has changed, it doesn’t make much difference.
Though I’ll quote part of the article about the transfer of part of the business between Sony and Murata. Link to the original article.

So if you bought a battery without Murata branding, it was either manufactured before the business was transferred or it is counterfeit.


First, here’s what these batteries are, according to the datasheet.
There are also VTC5 batteries (without the A suffix), and they differ slightly—for example, in weight. The VTC5A is a little heavier, and it also
has a rated cycle life of 500 cycles, compared with 350 for the VTC5 (before capacity drops to 70% of its original value).
Internal resistance is 10 mΩ, compared with 13 mΩ for the VTC5.
However, the VTC5A actually has slightly less capacity in Wh than the VTC5. If you’re interested, you can compare them in the VTC5 datasheet.

So, some general information.


Like all the previous batteries, the VTC5A also has a flat positive terminal. This is typical of the vast majority of branded batteries.
There’s a QR code, and it should be unique to each battery. If you have two batteries with exactly the same code, at least one of them is counterfeit.

According to the markings, the production date is encoded as follows:
The first letter is the year of manufacture: X – 2015, Y – 2016, Z – 2017, A – 2018, B – 2019, and so on.
The second letter is the month of manufacture: A – January, B – February, C – March... J – October, K – November, L – December.
The third and fourth digits are the day of the month the battery was manufactured, from 1 to 31.

The batteries reviewed here are marked 5AA13AF04S, which means 2018, June 4.


The dimensions match, and the weight is slightly higher. The datasheet gives an average of 47.1 g; mine is almost 48 g.


Typical internal resistance at 1 kHz is around 10 mΩ, and I got a similar result.


A “break-in” run with a capacity measurement, especially since the discharge current here is 0.5 A, which corresponds to 0.2C.
The batteries were initially charged to about 30%.


Next, I ran more accurate tests using an EBC-A20 load and a battery holder with a four-wire connection.


At this point, a bit of confusion came up. At the beginning of the datasheet, the nominal and typical capacities are listed as 2600/2500 mAh at 0.2C, with discharge down to 2 V. But later in the same datasheet, the figures are given for discharge down to 2.5 V, which is a little confusing.


First, I ran two tests, discharging to 2.0 V and 2.5 V, and got 2529 and 2470 mAh, respectively. Since the results for other load currents were given for discharge down to 2.5 V, I used that as the cutoff voltage too, to keep things consistent.


The battery was tested in seven different modes.
Red — 0.2C — 500 mA
Orange — 0.5C — 1.25 A
Yellow — 1C — 2.5 A
Green — 2C — 5 A
Light blue — 4C — 10 A
Blue — 6C — 15 A
Purple — 8C — 20 A



Battery temperature at the end of discharge at 10, 15, and 20 A.


The figures are slightly lower than the manufacturer’s claims. I’ll refer to the datasheet again to figure out why that might be.
The thing is, these batteries use a slightly different charging algorithm from the one usually used.
Test results are most often given for the following algorithm: charge at 0.5C up to 4.2 V, then stop when the charging current drops to 50–100 mA, depending on the battery type and capacity.
Here, however, the datasheet specifies charging at 2.5 A (1C) up to 4.2 V, but instead of stopping when the current drops, charging is stopped 2.5 hours after it begins.


Since my electronic load can’t do that and stops charging when the current drops to 100 mA, I decided to run an experiment using a separate adjustable power supply.


After the 20 A test, I charged the battery again using the EBC-A20 and got 2391 mAh. Then I connected it to the power supply, set the voltage to about 4.2 V (it actually came out to 4.21 V), and charged it for about an hour and a half, bringing the total charging time to the required 2.5 hours.
During the “top-off” stage, it took another 33 mAh, or about 1.3%, i.e. Previously, the battery charged to 98.7%; I expected it to take more.


A comparison test showed that the capacity with a regular charge and a full charge was 2387 mAh and 2406 mAh, respectively—a difference of just under one percent. Both tests used the same discharge current of 20 A.
Personally, I don't think the difference is significant. But if you measure capacity at 0.2C down to 2 V after a full charge cycle, the result should be around 2529 + 1% = 2554 mAh, which is much closer to the rated 2600 mAh.


Overall, I liked that the battery can essentially be charged to 98–99% in less than 1 hour 10 minutes at a 1C charge rate. That's a very good result.


I charged the second battery the usual way and discharged it to 2.5 V, just like the first one.


Battery temperature at currents of 10, 15, and 20 A.


Unfortunately, the load can handle a maximum current of only 20 A, while the battery is rated for a discharge current of 30 A.


Since I don't have an EBC-A40 load yet, which can handle currents up to 40 A, I had to bring in my main electronic load, whose maximum current is exactly the 30 A I needed.

To make the test as accurate as possible, I charged both batteries in the same device using the same charge termination settings.
I then connected the holder's power contacts to the electronic load and its sense contacts to a multimeter.
I reset the Ah counter, started discharging at 30 A, and measured the voltage drop across the wires and terminals: about 0.57 V.
I stopped the discharge, set the cutoff voltage to 1.93 V (2.5 - 0.57), and started the test.


The results were 2402 mAh for the first battery and 2398 mAh for the second.


And, of course, here are the battery temperatures at the end of the test. The first was a little cooler (98.5 degrees), most likely because the test was paused. The second was discharged in one go and heated to over 100 degrees.
The third photo is just an overall view of the “test setup.” Besides the battery, you can see that the wires get quite hot too; their cross-section is only 2.5 mm².


The test results surprised me a little. The batteries are clearly genuine, were manufactured less than a year ago, and perform well at discharge currents up to 30 A, yet I still couldn't get their rated capacity.
For example, according to the datasheet, capacity at a discharge current of 20–30 A should be 2470–2500 mAh. I got about 2400 mAh. I assume the result is lower because of the “simplified” charging algorithm, and that the actual capacity should be 1% higher (or even 2%, let's say), giving a maximum of 2450 mAh.
I don't know why. I noticed a slight discrepancy right from the start and recalibrated the load, but the difference was less than 1% at 0.5 A (the load has coarse calibration steps at low currents), and just 0.2% at 10 A.

That's all for now. As usual, I'll be glad to hear your questions and comments.