Fnirsi HRM-10 Battery Impedance Tester and Milliohm Meter

Yesterday, a package arrived with the new Fnirsi product, a battery impedance meter. I spent most of today getting to know its features, running some tests, and writing a review. I’ll say right away that I have a lot of work and little time at the moment, so I’ll keep this relatively brief.

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I placed the order on June 11, and by June 24 the box with the device was already at a Meest Express pickup point. That’s pretty fast, in my opinion.
The only thing I can complain about is that the box is rather large, and the device’s own packaging was just rattling around inside. Even a piece of bubble wrap didn’t help.
The packaging, by the way, looks very impressive—and is somehow rather large. I expected it to be smaller :)


Everything inside is great too: the device sits in a soft tray, with the cables underneath.


The package includes:
1. HRM-10 meter
2. USB Type-C to USB Type-A cable for connecting to a PC.
3. Cables with alligator clips
4. Manual.


The manual is multilingual. It includes Russian, but unfortunately I couldn’t find Ukrainian :(


The specifications, as I mentioned, are very close to those of the YR-1035.


1. USB cable: thin and short, but there’s no need for anything longer. It’s used to charge the battery and access saved data.
2. Measurement cable.
3. The device connects via a four-pin connector; the black section is 9 mm in diameter.
4. There’s a pair of alligator clips at the other end, providing a Kelvin connection.



This photo isn’t really necessary, but it’s amusing: the manufacturer even went to the trouble of making a bag with a special hole for the protruding connector :)


It looks nice, with absolutely nothing to complain about here. It sits well in the hand, and the case is clearly sturdy. I don’t have a YR1035, but I do have my trusty 1030, which looks the same. The HRM-10 is clearly better, no question, no “buts.”


The measurement cable connector is on the top edge. There’s a USB port on the right side, with a charging indicator hole below it and, further down—almost at the bottom of the right side—a reset button hole.


There are rubber feet on the bottom, plus a small but nice touch: a hole for hanging the device on the wall.
It also has a stand that lets you prop the device up at an angle. That’s handy, but there’s a catch: although the measurement cable isn’t very stiff, it is fairly thick, so it can easily tip the relatively lightweight device onto its side. I used it in the normal position, simply lying on the table.


Front panel.
There’s a large display at the top, and farther up on the right is an additional LED indicator. In sorting mode, it lights up green for a second after a successful test. If the test fails, it flashes red twice, while the buzzer beeps in sync. Really handy!

Below are five buttons:
1. Left/right; these also let you enter and exit the menu.
2. Up/down, for decreasing/increasing values and selecting the parameter to adjust.
3. The center button turns the device on and off, confirms selections, and activates Hold mode.


When you turn it on, the manufacturer’s logo appears, then the first time you start it up, you’re asked to choose a language. There are two options: Chinese and English. Once you’ve selected a language, this prompt won’t appear again, but the setting is available in the menu.


1. When switched on, the device enters its main mode for measuring voltage and resistance, with both ranges set to Auto. Use the up/down buttons to select voltage or resistance and switch to manual range selection.
2, 3. The menu is quite extensive, although in practice you’ll probably only need the first two items for typical use. Exiting some of the auxiliary modes is a little awkward.
4. Sorting mode. This is simple and convenient: select the voltage and resistance ranges. If the connected battery (or resistor) falls within those ranges, it’s marked as “test passed”; otherwise, it’s marked as “test failed.” The results are also saved to memory; more on that later.
5. Test result memory; sorting test data is recorded.
6, 7. Voltage and resistance calibration. If you don't have accurate instruments, don't even think about going in here.
8. Buzzer volume adjustment. I set it to 10% right away.
9. Set the date and time.
10. Display brightness. I left it as is, at 100%.
11. Automatic shutdown time. I set it to 15 minutes.
12. I thought I’d set everything, but here’s the “catch”: I adjusted the time and saved it, but after turning the device off and on, it had reverted to the original setting...


Now for a few tests.
First, a check of voltage measurement accuracy. The device was connected in parallel with a multimeter to a bench power supply. I set the voltage in a 1-2-5 sequence. Since the power supply, the multimeter, and the device under review all have a resolution of 0.1 mV, I tested from 0.1 mV to 59 V (I couldn't go any higher because the multimeter's resolution dropped).

As you can see in the photo, the device under review doesn't display anything below 50 mV, but above that its readings are practically identical to my multimeter's. A noticeable difference only appeared right at the end. I'd say it passed the test.

So it uses all the ADC digits, but can't measure below 50 mV.



Resistance.
The device can certainly be used as a milliohm meter, and will be especially useful for measuring the resistance of low-ohm shunts. On the lowest range, the resolution is 0.01 mΩ.
I measured special four-terminal shunts rated at 1, 2.2, 6.8, 10, and 47 mΩ, with a 0.5% tolerance. There is a little bit of fluctuation, which I'll get to later.
I also checked some standard resistors rated at 0.33, 0.47, and 75 Ω, with a 1% tolerance. These results also look perfectly reasonable to me.


About that fluctuation: when measuring resistor values, the least significant digit fluctuates by about ±1.5–2 counts. I consider that acceptable, although I don't recall seeing this when measuring battery impedance.


Measuring battery impedance.
Connecting alligator clips to ordinary cylindrical batteries is extremely awkward, so I had to use a universal holder. Besides, the clip tips fit perfectly into the connector :)


I tested eight batteries and compared them with my 1030. There was a small difference in every case: the 1030 readings were always slightly lower than the HRM-10's. Perhaps the 1030 has drifted over time—it's getting on in years—but I can't say for sure.
On the other hand, personally, absolute accuracy matters less to me than relative accuracy.


While I was at it, I measured some 230 Ah Calb batteries, first one cell and then the whole battery. Interestingly, the difference for a single cell was the same as in the earlier tests, but when measuring the battery, the HRM-10 gave a slightly lower result, though probably within the margin of error.

By the way, I want to emphasize the correct way to measure the impedance of batteries like these. Clipping onto the bolts is certainly more convenient, but it's completely wrong: you need to clip onto the aluminum contacts themselves. You can see this in the last photo. This is important!


Sorting mode.
I tested six batteries in a row. The settings were left at their factory defaults, since I just wanted to check that the feature worked.
The settings were: voltage from 3 to 4.5 V, impedance from 10 to 100 mΩ.
One of the batteries failed because its impedance was below 10 mΩ, outside the set range.


The device automatically saves test results to a CSV file. You can download it by connecting the device to a PC, where it will appear as a flash drive.


By the way, there's nothing stopping you from using the device to measure capacitor ESR, too. It only works at 1 kHz, but even so, that's much better than simply measuring capacitance, and it's more informative as well.

Just out of curiosity, I compared a few samples with my XJW01. The results seem quite reasonable to me. There is some difference, of course, but it's well within acceptable limits, especially for a device that doesn't even claim to have this feature.


In my reviews of the 1030 and 1035, I showed the voltage waveform at the device terminals in different modes. I wanted to do the same here, but it turned out that this device's waveform is exactly the same in every mode. This was measured with the circuit open. If you think it should be measured some other way, let me know.



And of course, let's take it apart.
The device is very easy to disassemble—almost surprisingly so.
First, unclip the tabs around the front panel, plus one in the center. They come off quite easily.


Next, remove the six self-tapping screws and take off the top half of the case.


The battery has a capacity of 1 Ah. After putting everything back together and preparing the photos, I noticed an indentation in the battery left by a wire—not good. I'll have to take it apart and check this, and I recommend you do the same.


The circuit board is neat and somehow... half empty. It looks a bit cheap :)


And here is the entire measurement section. It also has a pair of capacitors, just like the 1035, whereas the 1030 has none.


A closer look at the measurement section. The 4056 chip on the left charges the battery.


1. An unidentified circuit near the battery connector. At first I thought it was protection circuitry, but the battery itself has that, so it's unclear what this is.
2. A buzzer and... an RTC module. And here it's completely unclear how the time gets reset on a device with a separate RTC. A mystery. I've seen something like this before, though: a software bug where I set the time, but it doesn't actually get written to the RTC.


Conclusions.
I liked the HRM-10 as a measuring instrument. You can definitely use it as a proper instrument, not just a display, although it does have a few bugs.
For example, the clock resets. Another issue: when setting the time, the up/down buttons work in reverse—the top button decreases the value, and the bottom one increases it. But when setting parameters in sorting mode, everything works correctly.
Speaking of sorting mode, it's implemented very well. The visual and audible alerts make it even more convenient, so you don't even need to look at the device. Automatic saving of results and the option to export them easily are handy, too.

So far, the problems I've found are software-related, and I think they'll be fixed in a new firmware version. I'll have to write to the manufacturer.

In short, it's definitely worth the money. I'll go further: if you use a 1030 tester, it's worth upgrading. If you have a 1035, that's up to you—the specs are very similar, but the HRM-10 has a much better display and a more convenient sorting mode.

A reminder: the HRM1088 promo code should be valid through June 27 and gives you $3 off. The price has gone up to $40, though, but you can find AliExpress coupons now, so it's still worth buying.
That's all from me. I hope you found this useful.