Review, Teardown: Askborg ChargeCube 20800mAh Powerbank (M021)

When it comes to power banks, while some users are content to have a moderate-sized unit that charges their phone a few times, there are other users who really demand as much capacity as practical. For those users looking for 20,000mAh and above, the number of options are more limited and the price rapidly escalates.

This post looks at the Askborg ChargeCube 20,8000mAh power bank, a power bank featuring two USB outlets, one with “SpeedID”, an LCD display and a reasonable price. The unit was supplied directly by Askborg under review challenge terms for a thorough test.



The unit was packed inside a wood-pulp coloured cardboard box with a white cardboard wrap-around. The logo and branding is on the front.


Support information is provided on the rear.


The specifications are provided on the side. The unit has a model number of M021, with a 5V 2A input and a claimed 20800mAh capacity.


Inside the fold-open cardboard box, the unit sits inside a folded cardboard frame for protection in shipping. Unfortunately, due to the weight of the unit and the stresses of international travel, the cardboard was badly tortured. That being said, the unit did survive without any damage.

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The unit has a black aluminium body with rounded sides, as is common with other power banks. The size and shape suggests the presence of eight 18650-type cells, each with a 2,600mAh capacity for the 20,800mAh capacity. This unit features an LCD to indicate charge status as a percentage, as well as charging or discharge status. The LCD is backlit with a blue LED when the button is pressed. The logo is etched into the front, with the specifications on the rear.

2016082316588287The top side has a plastic facia with a single button to power-up and check the unit’s capacity. The unit auto-senses loading on the ports and starts up automatically. Two outputs are available, with the one nearest the power button featuring the SpeedID capability, and the one further away claiming “2.1A” output. The charging input sits in-between the two.


Aside from the unit, a fold open leaflet is included, with a small blurb on the SpeedID feature and a short microUSB cable with unknown wire gauge. The cable does have all pins connected and can be used for data synchronization as well.

Performance Testing

This section will look at both results of testing and subjective opinions from using the power bank in a day-to-day situation.

Delivered Capacity

Tests of the delivered capacity were made with the same apparatus used to test the majority of the power banks.

Load (mA) Run Capacity (mAh)
500 1 18683.89969
500 2 18663.34003
500 3 18677.61891
500 4 18624.39555
500 5 18623.74813
Mean 18654.60047
Range 60.15156036
StDev 28.84820926
Load (mA) Run Capacity (mAh)
1000 1 18046.5039
1000 2 17984.35378
1000 3 18116.31793
1000 4 18187.75547
1000 5 18194.9656
Mean 18105.97933
Range 210.6118231
StDev 90.88850731
Load (mA) Run Capacity (mAh)
2000 1 16658.9234
2000 2 16752.38394
2000 3 16756.05647
2000 4 16642.02521
2000 5 16766.02669
Mean 16715.08314
Range 124.0014705
StDev 59.49114356

Based on the delivered capacity in the testing, the unit is quite likely a genuine 20,800mAh power bank, delivering an average of 18,655mAh at 500mA, 18,106mAh at 1A and 16,715mAh at 2A on a 3.7V nominal voltage basis. Assuming the cells are 20,800mAh results in an efficiency of 89.6% at 500mA, 87.0% at 1A and 80.4% at 2A which are reasonable figures, considering that there may be 1-2% extra losses in the cabling of the test rig. The range of the results is a little higher than usual in the case of the 1A results, which were the first run, which may reflect controller uncertainty around the cell capacity.

Because of the large capacity of the power bank, testing a single run can take two to three days to complete. Now I know why very few people do reviews like these …

Output Voltage Profile


The output voltage was maintained within the USB requirements of 4.75v to 5.25v throughout, with the exception of towards the end of discharge where the voltage dropped somewhat gradually over a span of time. This was, however, displayed on the LCD as a flashing 0%, so it probably is intended to extract the last possible bit of charge before the unit shuts off, and being out of spec is not unexpected. The unit does disconnect the cells on end of discharge and the output falls to zero. During discharge, the voltage does have slow sawtooth-style movements, likely due to the limited granularity of duty cycle adjustment in the switching converter.

Output Ripple and Noise


At 500mA loading, ripple frequency was 122.6khz with a peak-to-peak voltage averaging 123.1mV with a transient “blip” every switching cycle. This is roughly the same level as many “stock” chargers.


At 1A, the switching frequency was 149.2khz with ripple reached a peak-to-peak voltage of 149.8mV. This is around the same level as stock phone chargers, and is considered safe although is not the “quietest” output around.


At 2A, the switching frequency was 161.4khz and the ripple voltage reached 233.5mV peak-to-peak, with the peak transients being the main offender. Without the transients, the ripple would have been similar to the 1A case. This is somewhat borderline – it’s higher than that offered by many stock chargers, but even some branded power banks have been seen putting out higher ripple voltages. It is probably quite acceptable, although ideally, I would prefer staying to <=150mV.

Charging Current Profile

Charging current was measured using the home-made USB current shunt and Keysight U1461A meter combination.


As the unit claimed a 2A input, I first tried charging the unit with a generic Qualcomm Quick-Charge 2.0 compliant charger with a 2A output at 5V. Unfortunately, charge current topped out at 850mA resulting in a long charge time of 23 hours and 48 minutes.

Because of that, I tried using an Apple iPad 10W (2A) charger, seeing as this is probably a common alternative it may have been optimized for. While charging was indeed faster, it didn’t use the full 2A capacity. It took 16 hours and 36 minutes to charge, and this may have been because of sensitivity to cable/contact resistance.

As a final test, I chose to try my Xiaomi 2A mobile phone charger, which successfully allowed the unit to draw just above 1800mA (the expectation for a 2A charger) and complete charging in 13 hours and 47 minutes.

Charge termination occurs at around 200mA input, and charging appears to be based on a switching converter. This would correspond to a termination current of about 34mA per cell, which is a little lower than the 100mA normally expected for most 18650 style cells.

Subjective Opinions

In my opinion, the Askborg PowerCube seems to be quite an attractive product based on its reasonable price. It is no-frills when it comes to inclusions and manuals, and it seems to have some contradictions – for example, the webpage seems to claim:

Exclusive SpeedID Technology: Detects your device to deliver its fastest possible charge speed up to 3 amps per port or 4 amps through three ports.

This is obviously not possible as the unit only has two ports and not three. It also claims in its manual that it weighs 455 grams, but in my own testing, it weighed 492.7 grams. This is consistent with the website claim that it weighs 493 grams – however, understating the weight in the manual might mislead some consumers, especially travellers with limited carry-on baggage who might need every last gram. The manual is brief but contains useful hints – such as recharging the power bank periodically to maintain performance. It also has a 18-month warranty which is a little longer than other products in this class.

Travellers might be slightly less satisfied with the 8-cell design using 2,600mAh cells. This leads to a higher weight and larger physical size than designs with more premium 3,400mAh cells from Panasonic (where six cells would give 20,400mAh). Accordingly, such cells command a significant price premium in return, so this is likely a compromise to reach such a competitive price-point.

While in use, I suffered no compatibility issues with my devices, namely several Android mobile phones and tablets, an Apple iPad and a Sony Playstation Vita. Charging rates monitored by a charger doctor were able to see about 2-3A total across the two ports – I wasn’t able to see 4A even with two tablets connected, possibly due to limitations in voltage drop. Under heavy loads, the unit did warm up slightly, but this is expected.

The LCD display was helpful in diagnosing remaining capacity and is more granular than most LED displays while consuming less power in operation. It’s not perfectly linear, but it’s pretty good. The biggest disadvantage is its limited viewing angle, which makes it hard to read when it’s placed down somewhere without tilting it to the right angle to maximise contrast.

While using it, I also found that the unit is not capable of synchronous charging and discharging. This may be a desired feature in some rare cases, but it seems this is not supported with the outputs shutting down as soon as a charger is plugged in.

It would be nice if the unit offered Qualcomm Quick Charge 2.0/3.0 abilities to more rapidly charge from the wall, as its large capacity makes overnight charging only possible where the adapter and cable are well matched. If it offered this ability, it could boost charging rates significantly and cut recharge times. Alternatively, in the case of QC 2.0/3.0 output, it could charge connected devices quicker, however, it seems likely that such a design would be more costly.

The output USB ports did feel a little “loose” and didn’t grip onto the connectors as firmly as I would have expected. On some cables, this resulted in slightly intermittent contact which could “wiggle out” if placed in a bag while walking around. Bending the USB connector shells slightly improved this.


Taking the unit apart is not particularly easy. As it turns out, both ends had their plastic fascias glued on in some way – the top using super-glue, and the bottom using something akin to liquid nails.

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I started by removing the bottom, which revealed that inside, the cells are very firmly siliconed into the body. This keeps the cells from moving around, which is great, but complicates taking the unit apart and identifying the cells. Even with copious use of a thin knife to cut through the silicone, I was not successful in extracting the batteries because there’s even more silicone inside.


Extracting the circuitry at the top required removing the LCD protective window first and then sliding out the capsule at the top.


A look at the PCB shows that it has some flux residue and a solder splash near the rear of the right USB port. More attention to manufacturing might be warranted. The wires to the battery pack are also slightly thinner than optimal. The batteries are well insulated with cardboard, and it seems they have been faced so that negatives of all eight cells are facing towards each other at the middle, and the positives are facing top and bottom, bussed together with a cable.

Because they were siliconed in place, I was not able to identify the make and model of cells used in the power bank. That being said, it appears that all eight cells are connected in parallel with no additional protective devices, which could be problematic if one cell were to fail as the other cells would dump into the failed cell limited only by (potentially) the PTC on the cell. There was no pack thermistor or additional one-time fuses visible. This is a common arrangement in lower-end power banks.


The controller is identified as a Shenzhen Legendary Technologies LDR5409 integrated power bank controller. According to the Chinese datasheet, it appears to be an LCD driver and power bank controller in one, and was designed to produce a 5V/2.1A output with under 100mV ripple at 2A. Other key specifications include a 3A output cut-off, >=92% efficiency at 1A and >=88% at 2A. That being said, it is possible that this design has modified the current sense and component values to squeeze more current out of the converter.


The other side of the board has the backlit LCD module, with a few ICs including the regular 8205A MOSFETs, DW01A Li-Ion protection IC and 9926A/DN1519A (MOSFET?) packages. A single un-enclosed inductor is used, suggesting a single rail design which the two ports share. As a result, the actual achievable current is not clear and will depend on just how the converter has been configured.


There is virtually no circuitry hiding underneath the LCD screen.


The Askborg ChargeCube 20,800mAh power bank is a very reasonably priced unit that appears to deliver the promised level of capacity at a sufficient voltage, with an informative LCD display, physically robust build, and trouble-free compatibility with my tested devices. The unit is backed up by an 18-month warranty for peace of mind, and comes with a charge cable.

Rather unfortunately, the unit doesn’t support Qualcomm Quick Charge capabilities, which is something it could really benefit from due to its large capacity and hence longer charge/discharge times. Its USB ports were slightly loose, and internally, the soldering quality left a little to be desired. The absolute maximum current delivery across the two ports was not established, but it appeared to be a single-rail design. The ripple voltage at 2A loading was slightly elevated due to the presence of switching transients at the peaks. I was unable to confirm the supplier of the cells, and the long-term durability of the unit as that would really depend on many factors.

That being said, it would not be fair to expect more especially when it retails for US$30.99 on special, as you really are getting a lot of usable capacity for your dollar. Readers interested in purchasing the Askborg ChargeCube 20800 can do so via Askborg’s Amazon stores (US, DE). Thanks to Askborg for supplying this sample for review.

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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2 Responses to Review, Teardown: Askborg ChargeCube 20800mAh Powerbank (M021)

  1. Kerry Lourash says:

    Was just searching Newegg and the automotive jump start packs run from 8,000 to 60,000 mAh! So 20,000 should be capable of starting a car with the right circuitry! Given the problems with hoverboards, laptops, and phones, I’d put safety high on my criteria. Maybe some company that could be counted on a recall, if it came to that.

    • lui_gough says:

      Things get a little complicated – there are lots of lies as well when it comes to the low end of the market. I’ve personally tested 30,000mAh power banks that were only about 5.000-6,000mAh of “real” capacity using no-brand cells and of an equal volume to this unit, so the numbers they put on their package are not always gospel.

      The next thing to be concerned about is that “lithium” comes in different flavours. For higher capacity storage, say powering laptops and devices in general, normally a cobalt chemistry electrode is used (ICR type cells). These cells absolutely cannot tolerate extreme current draws or they end up exploding. As a result, they’re typically used in 1C or less scenarios (e.g. a 2Ah cell drawn at 2A maximum). High current draws are enabled by nickel/manganese chemistry electrodes (IMR/INR type cells) which are used in say hobby R-C kits where sometimes they have the ability to be drawn up to 40-60C (so a 2Ah cell deliver 80-120A of current!). These are “traditional” lithium ion, so mistreat them and they’re vulnerable to explosions.

      Newer jumpstarting packs tend to be built using lithium-iron phosphate (LiFePO4) chemistries which are also popular with some power tool batteries, electric bicycles and some R-C toys. The main attraction is that these support high current discharge but are less likely to explode under abuse. However, they come with a drawback, as their nominal voltage is only 3.2V compared to the lithium ion chemistries which have 3.6-3.7V nominal voltage.

      This means that a 24,000mAh jumpstart pack using LiFePO4 chemistry (3.2V), if used as a USB recharger, has the same energy capacity as a 20,757mAh regular power bank using a ICR chemistry cell (3.7V). So when shopping, remember that energy (watt-hours) is the product of voltage and ampere-hours, and a larger ampere-hours rating doesn’t automatically equate to more power.

      – Gough

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