Review, Teardown: Xiaomi (Mi) NDY-02-AD Silver 10400mAh Power Bank

On an earlier post about power bank endurance and modification, Joy Test made a recommendation in the comments for me to test a Xiaomi, otherwise known as Mi, branded power bank. This is a Chinese manufacturer, which is most widely known for their high value phones.

I don’t normally chase products to review, as I often have no need to purchase so many products (especially of one type), but I was swayed by the rather positive things I have been hearing about them. Apparently, they set a high standard for other power banks to follow – lets see if that’s the case.

The most common unit is the NDY-02-AD Silver 10400mAh unit. The unit itself is listed for RMB69 on their website, which should be around AU$13, however, it’s almost impossible to find one at that price. Instead, I opted to pay a bit more for an Aussie seller to supply me the unit, at a cost of about AU$30. This might have been a wise choice, as it seems that counterfeit units are already hitting the markets.

Unboxing

My unit came in a nice matte cardboard box with a simple, understated, Apple-like grey print of their branding. The front had the logo, and the back had the mi.com URL.

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On the side of the box, there were barcoded serial numbers and the model number.

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On the opposing side, there is the product specifications and a scratch off verification code panel which allows you to check the genuine status of the power bank (more about this in the next section).

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Inside the box, there is a short flat USB micro-B charging cable that also has the data pairs connected, the power bank itself and a Chinese manual. Luckily, for such simple devices, there isn’t really a need for a detailed manual (and you can start using it right away). The ports on the power bank are covered up with a white piece of tape in transit.

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The power bank is made of an aluminium shell, with a similar finish to the “Apple” stuff. It’s quite amazing that there is such a quality feel to it, but it does also lend the power bank some level of protection against physical crushing. The ends, are made of plastic. Similar to the box, the front has the logo, the rear has the URL.

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The front end houses a power button you can use to check the power status of the power bank. Four small holes allow for a white LED indication to be shown. A single microUSB B connector is used for charging, and a single USB-AF connector is provided for connecting the device to be charged. It’s a little disappointing to have just a single port, but for the price, it’s quite acceptable. If you need more ports, buy a second power bank! It’s also likely to offer the optimal charging condition as there is less risk of overload with just a single device connected at a time.

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The other end features the models and specifications for the unit with the capacity in large letters, so you can’t miss it. The capacity itself is rated at 3.6v, but all of my testing is based at 3.7v, therefore the efficiency figures derived will be slightly lower than expected.

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For the purposes of helping users detect a fraud (on the suggestion by a friendly reader from Germany), the weight of this unit was measured on a (cheap) set of scales at 252 grams.

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Xiaomi have made a lot of quality claims on their website, including the use of LG/Samsung/Panasonic/Lishen cells, up to 93% conversion rate, minimum 6200mAh actual output capacity with many rigorous ESD and 50kg physical/mechanical stress tests.

Specifically, they also claim the availability of over temperature protection, over-current protection, over voltage protection, automatic load detection, over current protection and PTC protection in the battery cells.

I hope that we can verify some of these claims in action.

Genuine or Not?

No doubt some purchasers may have issues with their power bank that lead them to question if their power bank is genuine. One way is to perform a visual inspection of the device, following information provided by online websites, such as this.

Another method is to verify the unique code on the scratch-off panel. To do this, you need to first scratch off the silver coating on the label with your fingernail or a coin, to reveal a 20 digit code.

As many people might not be familiar with Chinese, and neither am I honestly, I will guide you through the process pictorially.

Visit http://chaxun.xiaomi.com and you should be greeted with this screen. Click on the purple power bank icon.

SecurityCode-SelectProduct

Then enter your 20 digit code, in four sets of five digits, starting from the top into the boxes from left to right. Then answer the math problem in the box with Chinese characters and click on the orange submit form button.

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You should see a result screen like this if it is genuine. The screen provides a confirmation it is genuine, and the number of times the code has been entered. If the code has been entered many times, it is likely to be a fake. In this case, it has been entered one time (numbers from 1 to 10 in Chinese for reference: 一,二,三,四,五,六,七,八,九,十)

SecurityCode-OK

In case of it showing no tick, check that you have entered your number correctly. If you still have problems, then you may have been a victim of a fake!

Teardown

Opening the Xiaomi power bank is pretty easy. The first thing to do is to carefully pry off the white plastic facia on the USB port side. This is secured to the chassis by clips and double sided tape. There is a white strip of label paper attached to the LED holes – these act as diffusers, making the indicator much less glary. The indicators themselves light solid/flash during charging, but only periodically flash the battery status during discharging to save power.

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Then, you need to undo the four black screws that hold the black plastic shell in the aluminium chassis. Once it has been undone, you can give it a good shake and the innards should slide out.

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Already, it is impressive to see the insides of the power bank as one of the claims is immediately obvious – the black lead that leads from the PCB to the battery pack is an NTC thermistor and is used to sense the temperature of the battery pack. It seems likely that the over-temperature protection is no lie.

Another thing that is very impressive is the use of orange mylar tape, which is normally used in proper battery pack construction (e.g. in quality OEM laptop batteries).

The PCB itself is a nice blue colour, and looks well made. The white component near the negative, marked with a 10, appears to be a fuse, thus corroborating their claim of having over current protection in the cells.

Flipping it over, we can take a close look at the cells.

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There’s no lies here either, as it appears to be a genuine LG Chemical LGABB41865 cell. These cells are rated 2600mAh each, for a total pack capacity of 10400mAh exactly as stated. They didn’t even lie on rounding up… quite impressive. However, it seems that the cells do claim to be 3.7v, so by marking them as 3.6v, Xiaomi may be trying to gain a little bit more efficiency percentage in their literature.

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The terminal tab spot welding looks pretty decent, save for some nicks in the heatshrink and in the tabbing on the left side of the right-most cell.

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A closer look at the top side of the PCB reveals certain testpoints, and markings of PB02_MB_45_131230C. This suggests the PCB design may date from 30th December 2013. The PCB itself is dated Week 18, 2014. There is a fair amount of semiconductor transistors, diodes and MOSFETs on this side, as well as a 1 ohm SMD resistor, likely as a current shunt to implement over-current protection.

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Looking at the other side of the PCB, there are more assorted components, but most interesting is the use of an ABOV MC97F1204S 8-bit Microcontroller (Week 14, 2014) to control the whole operation, and the Texas Instruments/BenchmarQ BQ24195 charger and synchronous boost controller. No doubt, careful design using a quality solution like this should see good efficiency results. There also seems to be several multi-layer ceramic capacitors to keep the power quality under control, although one spot seems to be unpopulated.

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Curiously, they haven’t gone for a shielded inductor, instead opting for what appears to be a potted inductor. This is probably to ensure that there isn’t any coil vibration, thus limiting the audible noise generated. Also visible is the tops of the cells, and it seems that the heatshrink around the second cell from the left has been damaged during manufacture.

In all, it’s not a flawless construction, but it does imply a good quality design and attention to detail. It’s probably a good power bank based on the teardown alone.

Performance Testing

Performance testing was run based on the new rig and methodology used in previous tests. This included the use of a Keithley Model 2110 capturing data on voltage and current in dual measure mode, with the power bank loaded by a resistive test rig that I built myself. Data was recorded at a rate >1 sample per second, and integrated in software to determine effective capacity delivered to load with some losses (at most, a few percent) due to voltage drop in short USB lead and banana cables neglected.

Charging the power bank took about 5.5 hours using a 2A rated charger.

The capacity results are as follows:

Load (mA) Run Capacity (mAh)
500 1 9737.687794
500 2 9708.080865
500 3 9704.267875
500 4 9708.916742
500 5 9674.390384
Mean 9706.668732
Range 63.29741072
StDev 22.45487579
Load (mA) Run Capacity (mAh)
1000 1 9423.794566
1000 2 9460.384478
1000 3 9517.412918
1000 4 9455.731412
1000 5 9448.873489
Mean 9461.239373
Range 93.61835147
StDev 34.42950857
Load (mA) Run Capacity (mAh)
2000 1 8710.609887
2000 2 8726.19427
2000 3 8720.846757
2000 4 8620.342065
2000 5 8696.767613
Mean 8694.952118
Range 105.8522057
StDev 43.1906419

Keeping in mind that the calculations performed are assuming a nominal battery voltage of 3.7v rather than the 3.6v, at 500mA, the power bank put out a very commendable result of 9707mAh, for an efficiency of 93.3%. At 1A, this dropped slightly to 9461mAh, for an efficiency of 91.0%. At 2A, the resulting capacity was 8695mAh, for an efficiency of 83.6%.

Rebasing the calculations on 3.6v, as Xiaomi had published, brings the efficiency ratings up to 95.9%, 93.5% and 85.9% respectively.

It is very commendable that at no point did the power bank even near the minimum 6200mAh promised, and even at the 3.7v, at 500mA it was capable of reaching an efficiency slightly greater than the 93% claimed.

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A look at the voltage profiles suggests that operation at 500mA and 1A were a breeze, with the voltages holding relatively stable, fairly close to the 5v mark. At 2A, the power bank’s regulation began to suffer a little more, but still delivering very solid results without ever getting close to the 4.75v limit of the USB specs. In short, no problems there.

The ripple and noise performance of the power bank was a little perplexing. It seems the power bank operates in two phases – one where there is a fair amount of ripple for a short time, and the other which is a much longer phase with a lot less ripple. As a result, the ripple figures reflect the peak-to-peak average of the tall phase. I did not bother measuring frequency because of this.

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At 500mA, on the longer timebase, it is clear how there is a repetitive “noisy” period, and less noisy periods inbetween. The average peak to peak ripple is 91.73mV at the 5ms timebase, and 100.1mV at the 500us timebase (as it captures the spikes more cleanly). This is a good result, as it remains below the ~150mV p-p that most mains powered phone chargers put out.

xiaomi-1a-10ms xiaomi-1a-500us

At 1A, the ripple actually falls to an average of 18.89mV peak-to-peak at the 10ms timebase, and 23.78mV peak-to-peak at the 500us timebase. This suggests that the converter design may have been optimized for a 1A load range. This is surprisingly low, even below that of the ATX 50mV requirement.

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At 2A, the ripple grows again, to an average of 98.19mV peak-to-peak at 5ms timebase, and 106.9mV peak-to-peak at 500us timebase. This is still a mighty good result, still below the 150mV peak-to-peak of wall chargers.

Conclusion

I think the results speak for themselves. If you’re looking for an inexpensive, simple power bank that performs well, this is the one! It looks to be well designed, and feels like a quality item. It’s built around quality cells, and a quality power conversion solution and has a very good level of efficiency and output voltage stability. The noise levels are very acceptable as well. The fact you can get it at AU$30 or even less just boggles the mind.

I think it shows just how much China can be capable of, when they take some care to design a quality product, rather than just putting out something passable for cheap.

This one definitely gets my recommendation.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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18 Responses to Review, Teardown: Xiaomi (Mi) NDY-02-AD Silver 10400mAh Power Bank

  1. Perfectly executed post and tons of information. Loved it, Lui, honestly 🙂
    I’ve had both of them, a fake and a genuine. One won’t notice a difference if he gets the fake, but when having both in hand, the real one can be easily identified without a deep inspection.

    The original one hasn’t disappointed me at all, but the fake one works okay too although with half the backup of original 😛

    • lui_gough says:

      Thanks for the feedback, and thanks for your post as well in regards to spotting a fake. I’m not sure I’d be as comfortable having a fake myself, when I saw this thread over at miui.com:
      http://en.miui.com/thread-19104-1-1.html

      Maybe he was unlucky, but safety with power banks, especially cheaper ones, is not a given!

      – Gough

      • Those images augh.. I’m afraid of using my Fake one now :/

        Wish Xiaomi does something about it. There shouldn’t be so many fakes of a growing brand. Something seems to be wrong. Either because the company cannot meet the demand or selling a fake is a big profit especially while selling internationally via AliExpress or similar sites.

  2. Turnkit says:

    The conclusion is a little confusing. You said, “I think it shows just how much China can be capable if, if they took some care to design a quality product, rather than just putting out something passable for cheap.” inferring that they hadn’t but I thought the whole point is that they actually do take care with this product.

    • lui_gough says:

      Improved expression slightly – but yes, basically that was more in reference to the other Chinese efforts I had reviewed prior, many of which aren’t good at all. Part of it was to do with a typo, but it has been corrected to read:
      “I think it shows just how much China can be capable of, when they take some care to design a quality product, rather than just putting out something passable for cheap.”

      – Gough

  3. George says:

    I got a fake one off of eBay with a red PCB inside 🙁 . I can do some photos for you sometime of the fake if you would like? (Ive already done my own teardown!)

  4. Joy Test says:

    Hi Gough,

    I’m glad you did take the trouble to obtain and test one, and turned out very pleased with the result as well.

    Cheers !!

    • lui_gough says:

      Thanks for that – a tiny detail but definitely important. If you zoom in on the picture I have above, you can just see the Mi logo on my USB port as well.

      Thanks for sharing!

  5. Pingback: Review, Teardown: Xiaomi (Mi) NDY-02-AD Gold 10400mAh Power Bank | Gough's Tech Zone

  6. Paul says:

    Interesting read. Any chance of you comparing this to the Anker Powerbank of similar capacity in the near future?

    • lui_gough says:

      Dear Paul,

      As a hobbyist, I really only have a limited need for power banks which have been easily surpassed by the number I’ve reviewed already on this site. As a student, I’m also always on a “budget” too – so no splurging out randomly on products I don’t need. But that being said, if I ever do purchase one, or someone is willing to donate one for the cause, I would be happy to test and confirm their performance for all to see as it puts my test equipment (which I was lucky enough to have won) to good use.

      – Gough

  7. Pingback: Review, Teardown: Xiaomi (Mi) Mini Bluetooth 4.0 Speaker (NDZ-03-GA) | Gough's Tech Zone

  8. Just a minor error. The R100 resistor is actually 0.1 ohm not 1.0 ohms. The R is most always used as a decimal point. Great review – I bought one and love it – very good quality.

  9. Hi Lui, great post. Thanks. I have an original mi powerbank too but lasted for only about 7 months or so with normal use. Everythin is working well except that I cannot seem to charge my phone with it. Need to push in the usb really deep n tight and it works only at a certain angle. Any idea how this can be fixed? or reason for this? Don’t wanna throw it away yet. 🙁

    • lui_gough says:

      It seems like you may have a USB port which has “lifted” from the board, so the rear four USB contacts may have cracked their solder joints. Provided they have not lifted and or torn the traces, it should be a simple matter of applying a touch of solder to the four solder joints on the USB port, and probably a little more to the “tangs” on the side which hold the port down into the board. If the traces have been torn, you will have to get some wire, and scrape off some solder resist to make a connection to the trace directly, like I did in this article for a USB key: http://goughlui.com/2015/07/31/project-physically-damaged-usb-drive-repair-data-recovery/

      Otherwise, your USB port may be a little loose, or your cable’s A-port may be a little loose as well. You can check this by testing different cables, or bending the A-connector’s shell inward slightly. In all, it should be a decently simple repair, so good luck!

      – Gough

  10. Muhammad Usman says:

    Me from Pakistan. My powebank is not getting charging because it charged too much, one hour more as usual charged. After this not working. Led lights turned off. I think it is burnt out due to excessive charging. But now I want to repair it. Me living in Peshawar-Pakistan. So identify what is the main problems.

    • lui_gough says:

      You may have a defective product, or a broken counterfeit copy. The original Mi power bank is pretty much protected against most faults – it cannot be overcharged. I will repeat, there is NO WAY it can be overcharged – even leaving it connected to the charger for DAYS. No output may be due to a broken cable, broken USB connector solder joint, or a shorted output due to a bad cable or scrap of metal that has fallen into the connector (and has thus triggered the protection mechanism). Pressing the power check button resets the internal circuitry and electronic protections – if the LEDs do not come on, chances are you have a problem on the cell side.

      You should disassemble the product, check the joints, check the cell voltages, and check the fuses on the board.

      – Gough

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