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

This post comes to you thanks to a generous reader from Germany (thanks Tobias!), who decided to contribute a power bank for testing. Unfortunately, the reader didn’t tell me what it was before it was dispatched, and it turns out to be another Xiaomi (Mi) 10400mAh.

In my last review of the Xiaomi, I reviewed the silver coloured edition which is the most popular one. However, the Xiaomi also comes in a range of other colours at a slightly higher cost – this one is a golden one.

While the colour of a product shouldn’t affect its performance, I decided it was worthwhile testing this unit for several reasons. There can be subtle build differences and revisions in products which can affect performance, and there might be quality control issues worth highlighting that only manifest themselves after analyzing several units. Statistically, having just one sample isn’t particularly significant – so lets see if Xiaomi can repeat their stellar performance again.

Unboxing

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This power bank arrived in a matte cardboard box, identical to that of the silver one. A notable difference with the silver one is the use of the xiaomi.com URL, which indicates this is probably an older unit. Newer units are marked with mi.com instead. This one also had a stock tracking barcode label which appears to be for the distributor/reseller’s use.

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The side of the box has a serial number (top) and UPC barcode (bottom) along with the model number.

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The other side is adorned with specifications, and the official verification seal. I did scratch off the silver coat and verify the numbers underneath at chaxun.xiaomi.com, where it correctly verified as genuine, as the first time the code had been entered.

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Included is the power bank, a Chinese manual and a USB micro B cable. The micro B cable had no Xiaomi logo, and had all wires connected for both data transfer and charging, which is another indicator of genuine status. The finish of the golden power bank is to a high standard, identical to that of the silver one. The front is adorned with the Mi logo, the rear features the xiaomi.com URL.

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The ports are buff coloured, and a Mi logo is seen inside the USB-A connector indicating, again, its genuine status. The specifications are printed in light grey on the other side of the power bank, and the indicator LEDs are small. All good signs!

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According to my not-so-trusty scales, this unit weighs 260gm, which is a little more than the 252gm of my silver unit, but might come down to slight changes internally and some added weight because of the finish.

Teardown

Breaking apart the power bank, an identical form of construction is seen.

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Internally, the circuitry is laid out identically to that of the previous power bank. Some slight exceptions are seen in the PCB silkscreening, which indicate this PCB was manufactured by a different company, to the same design specifications. From the date code, this PCB was made in Week 12, 2014 which is 6 weeks prior to the PCB in my silver power bank.

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The same sort of LG cells are visible inside, but the printing on the cells are all “wavy”. I’m not sure why this is the case, but the cells themselves appear to be genuine.

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The marking anomaly affects all the cells within this power bank.

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On the other side of the PCB, we can see everything is identically populated to that of the silver unit, down to the same unpopulated capacitor spot. The Abov microcontroller is dated Week 9, 2014, which is 5 weeks earlier than the one used in the silver bank.

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In terms of construction, some slight improvements can be made with the mylar insulation on the tabbing – there’s a slight gouge on the negative link, and the spot welding seems a little less consistent than in the other unit, but it’s still a good effort in general.

Performance Testing

The same methodology used in the previous review is carried forward, with the main interest in verifying the capacity of the power bank and calculating efficiency.

Load (mA) Run Capacity (mAh)
500 1 9747.957136
500 2 9761.970879
500 3 9764.186531
500 4 9762.0129
500 5 9742.946146
Mean 9755.814718
Range 21.24038552
StDev 9.666239966
Load (mA) Run Capacity (mAh)
1000 1 9276.94628
1000 2 9466.482107
1000 3 9469.5623
1000 4 9475.603401
1000 5 9471.726582
Mean 9432.064134
Range 198.6571208
StDev 86.77706413
Load (mA) Run Capacity (mAh)
2000 1 8761.804708
2000 2 8760.62915
2000 3 8768.616895
2000 4 8735.541467
2000 5 8693.808093
Mean 8744.080063
Range 74.80880164
StDev 30.78258426

At 500mA, the usable capacity is 9756mAh, at 1000mA, the usable capacity is 9432mAh and at 2000mA, the usable capacity is 8744mAh. The recorded value of usable capacity at 1000mA may be slightly reduced because of the first run showing a ~200mA disadvantage possibly due to inconsistent charging (early termination). However, again, a very consistent charge termination was achieved for all other runs except the first.

Calculated efficiency figures are 93.8%, 90.7% and 84.0% at 500mA, 1A and 2A respectively, using 3.7V as the basis. Using 3.6V, the efficiency improves to 96.4%, 93.2% and 86.4% respectively.

Compared to the silver power bank, the resulting capacity figures are all within 50mAh! Likewise, the efficiency figures are virtually identical and the minimum capacity and maximum efficiency claims are all met.

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The voltage profiles are slightly different but exhibit the same level of stability over the long term and are all well within the USB voltage specification requirements.

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The rather Xiaomi specific “two-step” ripple is also present. At 500mA, the values are 84.16mV peak-to-peak at 5mS/div, and 91.56mV peak-to-peak at 500uS/div which is a commendable result, below 150mV of wall chargers. This is slightly less than the silver unit, but within expected sample-to-sample variation.

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At 1A load, the values are 87.5mV and 90.11mV respectively which is higher than the silver unit, but consistent with prior readings. It’s a good result, in fact, the silver bank’s result is a little suspiciously low.

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Increasing the load to 2A pushes the values to 108mV and 95.15mV respectively, which is almost indistinguishable from the silver power bank, and an exceptionally good value seeing as the ripple output is almost independent of the output current.

Conclusion

In a result I didn’t quite expect, the Xiaomi Silver and this Xiaomi Gold perform almost indistinguishably on capacity (within 50mAh), and ripple performance. This is good news, as it indicates that the quality control is probably quite good, and quality LG cells are consistent for capacity. Each of them has their slight construction quirks, but nothing too major.

I’d have to say this is another good score for Xiaomi. I am very happy with its performance.

About lui_gough

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3 Responses to Review, Teardown: Xiaomi (Mi) NDY-02-AD Gold 10400mAh Power Bank

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