Follow-up: USB Power Bank Tested and Repacked (5000mAh, 30000mAh)

I did some quick teardowns of the 5000mAh and 30000mAh power banks previously, and I found that the 5000mAh power bank seemed to be genuine, but the 30000mAh power bank is a bit unknown. One reader reported disappointing performance from the power bank, and I would be inclined to agree after some more extensive use.

But it’s hard to find out exactly how good or bad they are, without testing them under controlled conditions. Thanks to the element14 RoadTest program, I was the lucky recipient of a Keithley 2110 5.5 digit USB and GPIB Digital Multimeter which was perfect to run this investigation.

Test Setup

I built a configurable 2.5 ohm and 5 ohm equivalent ceramic resistor pack as a dummy load, hooked to the end of a piece of scrap USB lead. Measurements of voltage and current were taken once a second (roughly) with the dual-measure facility of the Model 2110.

After many many hours of testing, I ended up with a >10Mb spreadsheet from which I performed calculations upon to get to the bottom of it.

Capacity Result

Power Bank Test Results

We can see that the error due to the meter itself is tiny, but there is error from the leads. There is also errors due to differences in operating temperature, USB connector resistance, etc – but their effect on the final figure is unlikely to be even 1%. Variation in separate runs is “normal” as most battery packs are only specified to 100mAh accuracy with variation due to self-discharge and charge termination points.

For now, you can ignore the yellow result – this was after I rebuilt the pack (later on in this posting). We can see that we ended up with about 3800mAh at 3.7v for the 5000mAh battery pack loaded at about 1A (the port rated output) – this is due to losses in power conversion as heat (poor design?) and losses in indicator LEDs etc.

But worst of all, the 30000mAh packs loaded at 1A measured about 4000mAh at 3.7v of effective capacity. This isn’t much more than the 5000mAh pack! It’s physically much larger for no good reason at all.

Loaded at the 2A rate, the capacity drops to about 3800mAh at 3.7v effective capacity! The cells in the 30000mAh pack are literally rubbish!

Also disappointing is the efficiency – it seems that the 5000mAh packs have sub-optimal conversion efficiency at 1A loading. Properly designed DC to DC converters should be able to achieve 88-94% (or thereabouts) efficiency.

Voltage Result

USB Power Bank Output vs Time

The voltage result shows even worse news. These power packs fail miserably when loaded to around their rated current. Over 2.5 ohms, you’d expect 2A to flow, but instead due to the voltage droop and tolerance, we see only about 1.6A. So this test is already a little generous. The voltage provided by the packs loaded at their rated current (5000mAh at 1A, 30000mAh at 2A) all show voltages below the 4.75v limit (5v – 5%). It’s a wonder that devices are so accommodating to even work with them at all.

The 30000mAh pack does provide much better voltage figures when loaded at the 1A load suggesting it was designed for that load. Chances are, the difference in capacity may have come about from the heat evolved from the converter circuit and difference in efficiency as the voltage droop suggests the converter itself is overloaded and possibly noisy.

The legend is coded as follows:

  • First letter – battery design. A is 5000mAh, B is 30000mAh.
  • Second letter – battery number – I have two packs of each type.
  • Load Current – 1A or 2A (approximately, really means load resistance 5 ohm or 2.5 ohm).
  • Run Number – Some runs repeated three times to gauge accuracy.

Unfortunately, it was also discovered that the 5000mAh pack has a design flaw. It has no MOSFET cutoff at end of dicharge, and so the voltage abruptly drops from 4.6v to 2.3v, suggesting possible over discharge from incorrectly set end-point. Leaving a USB device attached after the pack appears depleted could further deplete the cells and damage them irreversably!

The 30000mAh pack disconnects its outputs to 0v when reaching its termination point – although we do need to determine the actual termination point voltage-wise to ensure safety for our Li-Ion cells.

Rebuilding the Pack

It was suggested that it might be possible to rebuild the pack – now while, in principle, I agree, soldering directly to Lithium-Ion cells are not advisable. I happened to find that it was possible, if one was careful, to solder to tabbed Lithium-Ion cells, so I gave it a go.

DSC_0001

I consider myself an intermediate at soldering – soldering to the cells themselves would be impossible as the cells would sink the heat away and cause damage to the cells. It would be best to use spot-welding, but I don’t have such equipment. I took the risk and ordered almost $100AU in Lithium-Ion Cells.

DSC_0003

I opted for eight Panasonic NCR18650B’s. These are now the world’s highest capacity 18650’s, rated at 3350mAh each. Even with eight, the best I could expect was 26800mAh – still shy of the 30000mAh it was “rated”. Also, the pack would look ugly. Not that it really mattered to me.

DSC_0005

DSC_0004

After some careful soldering, and lots of electrical taping – I ended up with this monstrosity. It was much heavier than the initial pack, and it takes a lot longer than 24 hours to charge. Luckily, the charger and converter are “voltage sensing” devices, so they don’t care about the change in capacity (or so it seems – it is yet to be conclusively determined).

Charging takes almost two days, and the LED indicator does sit on the first bar for almost a day, giving the impression that nothing is happening, but the PCB does get warm indicating the charging circuitry is working …

Rebuilt Pack

The improvement in run-time was phenomenal. The gauge now is inaccurate, displaying the single bar for a long time. As I soldered to the ends of the tabs, there was much less mechanical rigidity in the pack, so I used some Nitto electrical tape to bolster it. Since the solder is proud of the tab profile, I needed to bend the plastic slightly to shoehorn the whole thing in. But it works.

USB Power Bank Output vs Time with Rebuilt

The output is a bit lumpy, but it blows the competition away at the 2A load rate. It took almost ten hours at the 2A (1.6A) rate to finish it up. At the 1A rate, I could easily be waiting for a bit longer. I think it’s obvious why I couldn’t afford to make multiple runs – there has been much interest in this subject, so I wanted to get the word out as soon as possible.

I’m not quite sure why the output is lumpy – this could be sudden changes in contact resistance in the USB connector when heating/cooling, and or it could be discrete stepping of the duty cycle/frequency of the switching converter (although, I would expect much smoother steps in properly designed converters). Interestingly, both packs seem to eschew the use of more conventional dedicated IC drivers, and seem to utilize OTP microcontrollers to do the work – so this “mystery” may come down to the code and or limited PWM/output resolution.

If you head back to the capacity result table, you can see that I’ve used the nominal capacity of the Panasonic cells (I trust them) to derive a converter efficiency percentage for the 2A rate. Applying this to the existing eight cell pack gives me a reading of 632mAh per 18650 cell in the original pack. Waste of space!

Checking out the Original Cells

Since the original pack was so worthless, I decided to take it apart and grab a cell to pull the wrap off, hoping there’d be some clue as to who was behind the mess.

DSC_0007

But the cell is naked. I’m sure the manufacturer isn’t proud of what they’ve achieved.

DSC_0008

There is one difference to the cells – the ring that sits on the positive terminal is made of plastic rather than paper. Hmm.

DSC_0009

So there is such a thing as too good to be true. And it can be even worse than you were expecting, even if you were expecting a lie. Never underestimate the power of lies …

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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46 Responses to Follow-up: USB Power Bank Tested and Repacked (5000mAh, 30000mAh)

  1. Pingback: Review: Unbranded 30000mAh 2 Port USB Power Bank | Gough's Tech Zone

  2. k says:

    thanks for the review and update.

    just wanted to let you know that your work is being read and appreciated

  3. Chinoy says:

    So do you have any recommendations when buying a power bank? There are a ton out there!!

    • lui_gough says:

      Excellent Question!

      Unfortunately, as I don’t have an ‘infinite’ need for power banks, nor an infinite supply of money, I haven’t really tested enough power banks to find something of true quality. There are drawbacks in capacity and voltage stability.

      I suspect that one has to pay more and buy branded power banks if they want to ensure quality, capacity and longevity – but I can’t say for sure whether you get more if you pay more.

      – Gough

  4. Brad says:

    Thanks Gough. The tip about leaving the cord plugged in the bank and it depleting the battery explains why mine is loosing it to the point of being useless. Note to self: Unplug the device when charged and not in use. Cheers. Brad

  5. Nesar says:

    HAve some good ideas about those cheap skates. Thanks, really appreciated.

  6. Jaydog says:

    Thanks for the excellent review/breakdown Gough!

    The only one on the web (that I could find) that actually gets to the heart of the matter – most cheap battery packs are no where near their stated output and have little protection

    It would be interesting to see if a branded battery pack has a better build quality and outputs at the rated amount??

    Cheers Jay

    • lui_gough says:

      Dear Jay,

      Thanks for the comment – much appreciated. I would assume many of the branded ones will be somewhat better just because the brands would probably value their brand image enough to put it through its paces before slapping their name on it (or in some rarer cases, they would design it in-house entirely).

      That being said, as I’m not exactly in the market for another power bank – I’m not likely going to have any hard answers just yet. If someone or company would like to donate their products for testing, I’d be happy to oblige!

      – Gough

  7. magnip says:

    Hello thanks for a interesting read i have the 30000 model you reviewed only differance mine is black. Do you know how to stop or bypass the auto shut off because when my camera goes into standby mode it dosnt pull enough current to keep the power bank from going into sleep mode thus shutting my cam down. Also i know this post is old but if your still about could you confirm the lenth of the pack because im sure mine is even more of a con a 20000 model with a 30000 sticker on, i did rip it apart just as you did thats why i enjoyed your post but i have put it back together with a role of e tape like yours and dont want to tare it apart again unless someone can instruct me on how to keep the power block constantly on. thanks and sorry for long post just hope its relervant and in the right place

  8. Magnip says:

    Ok look like I was done mine has three cells a side never mind I thank you for a very swift response.

  9. Adam Gill says:

    I bought the same 30,000 power bank .. testing it out now …. will also change over to the 3,400mah or higher 18650 cells …. I’m not sure if all the 30,000 power banks will be rated as low as you tested ..

    • lui_gough says:

      Dear Adam,

      Of course, there will be variations in the stuff the manufacturers put into the power bank. One indicator of the quality is weight, another is the charge time and finally the obvious one is runtime. If it was 30,000mAh, you should be able to charge a Retina iPad (massive battery) about 3 times from dead-flat. The original cells I had couldn’t even do it just once.

      The 3400/3500mAh cells I used are the largest 18650 cells which are legitimate at this time (to my knowledge). Most of the other cells rated above, especially UltraFire, TrustFire, etc are all fake.

      Good luck with yours :).

      – Gough

      • Adam Gill says:

        Gough,
        I successfully did the transplant – it’s charging now …. will take a while – I’m using 3,100 mah made in Japan. Will add pictures when the testing is done – how to add pictures here? The charge is on no. 3 flashing position – it started on no 2 as there as some juice in the batteries when i bought them. As i am living in HK/China – I can source batteries if anyone interested.

        • lui_gough says:

          Dear Adam,

          Unfortunately, it doesn’t seem WordPress will allow you to embed images into your post, so I suggest you upload them to a web service like imgur and then post the links to the images in your comments.

          With such large cells, if you’re using eight, and you fully deplete them, you can expect charging to take almost 2 days to complete in my experience. While it may be possible to increase the charge rate with a resistor tweak, I’m not too sure of the actual make of the charge controller chip and whether the PCB might not have enough heatsinking for it. As a result, it can be a little annoying if you don’t have a dedicated Li-Ion charger.

          Aside from that, having eight cells parallel in two groups of four with no protection isn’t exactly the “best” thing to do to a bunch of cells anyway – but it certainly makes the pack perform more like you would expect.

          Glad to hear it went well!

          – Gough

  10. Zee says:

    Hi,

    Just a quick question. Can this device be charged and charge a mobile phone at the same time?

    Thanks

    • lui_gough says:

      No, not for the 30000mAh pack. By plugging in the power adapter while the pack is charging an appliance, the output is switched off.

      The 5000mAh pack is inconclusive. While the output remains on, the LEDs look similar for charging and discharging. I think it may be charging the pack, but as it charges slowly, if the output is used to charge a tablet and a phone, the pack may still be depleted to some extent. I will have to observe its operation further to determine whether it is capable of doing both charging and discharging at the same time, however, do note that this can contribute to “micro-cycles” which can also wear out Lithium-Ion packs.

      – Gough

  11. Bobby says:

    Great review.. it has amazing content and really clears up any misconceptions about this Bargain “Wonder product”.

  12. Ivan says:

    Dear Gough! Thank you for the review! Now I am sure I won’t buy such a 30000 mAh power bank. Do you have any experience with commercially easily available AA batteries that are supposed to be of 2500 mAh capacity? I am asking because if those are good, then with this little device https://www.powertraveller.com/en/shop/portable-chargers/back-up-business-travel/powerchimp/ I could have a nice 5000 mAh backup…
    Thanks in advance!

    • lui_gough says:

      Dear Ivan,

      In general, Ni-MH cells of 2500mAh capacity are likely to be the older type which have horrendous self discharge. As a result, they will lose a lot of their charge within the first week after charging, thus when you need it, it might already be pretty close to flat. The low-self-discharge sort, like the Sayno Eneloop are generally right on the dot with the capacity, and they’re about 2000mAh each.

      But hold on a sec – it seems there is a common misunderstanding as to measurement units, so let me explain.

      By itself, mAh (milli-amp-hours) is not a unit of energy but merely an indication of how much current a cell can provide for a given unit of time, in this case, an hour. This is an oversimplification, as it could have been measured at a rate other than an hour (e.g. five hours aka C/5 rate, twenty hours aka C/20 rate) and then converted back to the equivalent of the hour by multiplying by 5 or 20 respectively. Unfortunately, battery capacity falls if you start pulling charge at it at a higher rate.

      The unit of energy is Watts, or in this case, you can even use mWh (milli-watt-hours), and is the product of the mAh by the (average) nominal voltage of the cell chemistry. As lithium ion and lithium polymer have nominal voltages of 3.7v (mostly), and Ni-Mh cells have only 1.2v, you can see that a 500mAh Li-Ion has about three times as much energy in it as a 500mAh Ni-Mh cell. As a result, you cannot compare them directly. Even worse is that most power banks don’t explicitly tell you the nominal voltage the mAh rating was obtained at, so they usually use the lowest voltage they can, a single cell, which is 3.7v for Li-Ion/Polymer, so they can inflate the mAh value, despite the fact they could even be connected in series in some cases.

      As an exercise – does a 11.1v 5200mAh laptop battery have more charge capacity than a 3.7v 10000mAh power bank? Well the laptop battery has 57720mWh, and the power bank has 37000mWh, so it’s definitely the laptop battery but you might not have guessed it from the mAh figure alone.

      The second thing is related to the thing above – as the PowerChimp seems to use two 1.2v Ni-MH cells, it’s likely they are wired in series to increase the voltage. As a result, the voltages add, but the current capacity remains the same. As a result, you would have 2.4v x 2500mAh = 6000mWh of energy at the best. (Or if you think about it wired in parallel, which is unlikely, the answer will still be the same, because it’ll be 1.2v x 5000mAh. Intuitively, if you have two batteries, the total energy will remain the same, but depending on the voltage, the mAh rating could be different! If you divide this by 3.7v, you get the result that this is equivalent to a lithium ion/polymer power bank which can provide 1621.62mAh. Most Lithium-Ion power banks can provide much more than this.

      As a result, I cannot recommend AA based emergency chargers except for when you absolutely need the flexibility of being able to pick up AA batteries from any corner shop, or the fact you can pack a large number of them into a suitcase – e.g. travelling.

      Hope this clears up a very common confusion.

      – Gough

      • Ivan says:

        Dear Gough,
        Thank you very much for the detailed reply and the clarification! I was thinking of voltages and Watts as well, but did not go into so much detail, so I really appreciate your help. Some friend suggested me to use the Yoobao Magic Cube, which proved to be a very good value for money product to them (it is Li-Ion type). It is available in three versions, the strongest one being of 10400 mAh. I think I will go for that. Cheers

  13. Macoh Musada says:

    Hi also did what youve done.taken it apart and tried replacing the batteries. I first bought 2 18650 batteries just for testing if those batteries would work before buying 6 more. But when i connect my two batteries and plug in my galaxy tab. The 4 leds would just flash. Will it work like it used to if i placed all 8 batteries? Thanks in advance :)

    • lui_gough says:

      Are you sure your two 18650’s are connected correctly, fully charged and of high quality? None of that Ultrafire/Trustfire China rubbish?

      With just two, it should function just fine if the board has not been damaged or there is no other problems (e.g. short circuit, empty batteries). Adding more batteries in parallel increases the capacity, although at the cost of safety (in case of a cell failure). The behaviour of the power bank should not be altered if you used eight batteries, except for the fact it will last longer, and take longer to charge.

      – Gough

  14. Macoh Musada says:

    Its ultrafire haha. Sure of its not of high quality. Its hard finding good brands here in the philippines. So if ever. It wont really work with these fake ones?

    • lui_gough says:

      The problem with the cheap brands is that they lie drastically about the capacity. If you think you’re improving the capacity, chances are, you aren’t – or not by much and not for long (as they degrade quickly, most within their first year). Some of the cells have also been known to spontaneously explode, and thus, can be a danger.

      The main reason I can think of it not working may be due to high internal resistance from a bad cell – so when the power bank tries to draw the required current from the cells, the voltage on the cells drops too far and the circuitry shuts down. Maybe this is one reason for them paralleling so many “low quality” cells, to spread the load out. Or they’re simply not holding charge. Maybe you have a defective circuit. Regardless, do check they have been properly charged and properly soldered to the circuit – it should work, even if poorly, if the cells are any good.

      – Gough

  15. Macoh Musada says:

    Well i guess thats why mine wasnt workinb. Better get a orignal battery. I know the circuit still works because i have an adjustable power supply when i set it to 3.7 the circuit charge my galaxy tab. Anyway thanks for lettibg me realize that. :) what are the top great brands for 18650?

    • lui_gough says:

      I would generally recommend only the “big name” cells – e.g. Panasonic, Sony, LG, Samsung to name the best. They will have much better lifetimes, an accurate capacity, better safety and generally weigh more. Beware that there may be some counterfeits on the market.

      – Gough

  16. Macoh Musada says:

    Can i use those 18650 which can be obtained from laptop batteries?

    • lui_gough says:

      Depends. Most of the 18650’s from original manufacturer quality batteries are made from the companies listed before, but depending on how old they are, they may have lost some capacity. It will be more difficult to use them, as you will need to break them apart, spot weld tabs to them, and then solder to the tabs. Soldering to the batteries directly can be extremely dangerous, and the heat transferred to the cell can damage it.

      There are good looking copies of laptop batteries, which use low quality Chinese cells as well – those are unlikely to be much better than what you have now. Finally, some laptop batteries (depending on the shape) may not use 18650’s internally at all.

      – Gough

  17. Cristhian Macoh Musada says:

    Hi its me again, i got some sanyo 18650 cells from an old battery. i want to charge them, but dont know how to. could i use my becn power supply which can regulate voltage from 0-32v and regulate output current from 0-1.24 amps. can i use this to charge my 18650 cells?

    • lui_gough says:

      It can, although it may be slightly risky if you do not set the correct voltage or current limits. Charging lithium ion requires a CC-CV charging regime, which means that initially, the current is limited to a value (usually something like C/2 or less) and then finally, after the voltage begins to rise, then the voltage is limited as the current tapers off.

      Depending on the chemistry, generally the charging voltage limit PER CELL is 4.2v at the most. I would advise against setting it at exactly 4.2v if your supply is not accurate, overcharge can cause dangerous conditions (fire, explosion). You can probably set it to 4.0v and get a reasonably good level of charge. The current limit should be about 800mA or less. Then, as the charge progresses and the supply is in CV mode, when the current drops to a small value (below C/10 or thereabouts), you should terminate charging and not just leave the battery sitting at 4.0-4.2v (as some cheap Chinese chargers do, as voltage stress can degrade the life of the battery). If it doesn’t reach a low current after a prolonged period (4-5h), the battery may be dangerous as it has some internal shunting, causing loss of energy, and you should discontinue charging.

      BUT you should charge one cell at a time, and check the condition of the cells before attempting to charge. If the cells measure below about 2.3v, then they are severely over discharged and may have formed copper shunts internally. Charging these can result in future explosion due to internal short circuit and thermal runaway. If the cells measure about 2.5v-2.8v then you might be able to revive them but at a much slower trickle rate until it reaches about 3v per cell.

      I cannot be held responsible for what you do and don’t do, and the outcomes of your experiments. I advise you to do some research, as Li-Ion is not a “safe and friendly” chemistry like the others, which is why cells were and are difficult to buy individually outside of finished products. Any abuse can lead to fire and explosion which could burn down your house, or fill your room with black smoke. Make sure you find all the information you need and convince yourself you know what you are doing! Again, not my fault if you get hurt, or lose anything.

      – Gough

      • Cristhian Macoh Musada says:

        I guess that would be a last option cause i dont want to take the risk at first. i bought a charger for 18650 which outputs 4.2v @ 500mA. since it only can charge one cell at a time. i charge them 2 hrs each. and was able to get voltages for each is 3.9volts. can i modify the charger where ill connect it to my arduino to control it so when it reaches the peak voltage id make it stop. by doing that can i charge all of them at the same time? and also another thing. since i have the PCB of the powerbank i tried charging them through it but only outputs 130mA. i guess the power banks PCB not working anymore so any more suggestion i would love to hear. thank you :)

        • lui_gough says:

          It would take quite a bit of circuitry to modify a charger to work with an Arduino – you could isolate each cell from the charger with MOSFETs controlled by the Arduino, using the analog inputs for voltage monitoring, although you will have to calibrate this in case the values from the ADC are not as expected (as it can vary depending on the accuracy of the 5v power received by the Arduino).

          Low charge output from the power bank might be caused by a poor USB contact or thin low quality wire causing high resistance. Otherwise, it can be caused by a bad USB charger which cannot supply the correct current under load. Other times, it’s probably because the power bank charger IC has been configured with resistors that result in a low charge current so it takes longer to charge (thus, appearing to be a good power bank, as they typically take a long time to charge due to high capacity).

          – Gough

          • Macoh Musada says:

            So is there anyway i can fix the charging module of the power bank?

          • lui_gough says:

            Unfortunately, I have no idea what’s wrong and what can be done, especially because the ICs used are often not easily available, and being surface mounted, not easily replaced either.

          • Cristhian Macoh Musada says:

            about the circuit to control the charging can i use a relay instead of a MOSFET? the relay would function as a switch for the charge. when it reaches 4.2volts the relay would be turned on to stop the charging and ill add a temperature sensor when the battery would reach a hot temperature the relay would turn off the charger and let it cool down before turning it on again. will that work?

          • lui_gough says:

            You could use relays, however, due to the relay coil itself consuming significant current and back-EMF which occurs on de-energizing the relay, it is not appropriate to directly connect a relay to an Arduino output pin. You will need at least a back-EMF protecting diode AND a small MOSFET or BJT to handle the high currents required by the relay itself.

            Can you see why this isn’t really a superior solution? The other issue is that relays are mechanical, and they’re noisy. They can also be unreliable. So personally, my preferences nowadays tend towards using logic-threshold n-channel MOSFETs for my switching where it’s appropriate.

            Unfortunately, I don’t have the time to attend to every question you might have, as I am (despite how it appears) very busy – I suggest you do some research, as many hobbyists sites, especially those surrounding remote control cars/planes/boats tend to deal a lot with Li-Ion and Li-Poly, and might be better suited to helping you.

            – Gough

  18. 0xd020 says:

    I stumbled upon this post while searching for a power bank for my mobile RPI project. Excellent job! This saved me a lot of time and money.

  19. Phil says:

    Hi,
    Great info. I bought a 30000mAh Solar power bank, the type that come in several colours. They are very common on eBay. Anyway when it arrived I thought it to be quite light weight. On the scales it weighed in at 100 grams.
    So I opened it up and found mainly empty space with a battery that would be equivelent in size and shape to a 3000 mAh phone battery.
    Do you think this is some new tech high compact high capacity battery or have I been ripped off?
    Paid $16.00 for this but the seller says he’s going to refund my money. Got $1.00 back so far. Paypal case is looming.
    Would it be possible to install good cells and make this solar battery pack worthwhile or are the electronics no good either?
    Was thinking of using Sanyo cells made in Japan.
    Thankyou.

    • lui_gough says:

      There is no such thing as a “new” high tech battery that magically is 10 fold better. If there was, and it was affordable, it would be ubiquitous and certainly used by the latest generation devices, be it tablets or phones. It seems like you have been ripped off, and been sold much less than what you were promised.

      At times, you may be able to determine the result by reading the markings on the cell. It may give away capacity and manufacturer. But seeing that it weighs 100 grams, the best case power-to-weight for lithium polymer is 265Wh/kg … so … you’ve got at most 26.5Wh or 7,162mAh assuming the best of cases. Assuming the low-end of the scale gives 100Wh/kg, so you have 10Wh or 2,702mAh of capacity. Both calculations assume that all of the weight is in the cell.

      In general, I would have to claim that most conversion circuitry in cheap power banks are of poor quality and don’t put out clean power. My advice would be to steer clear of it altogether, it’s probably not worth your time and hassle to modify it at the risk of stressing or damaging your more expensive electronics (i.e. phone, tablet, etc).

      – Gough

      • Phil says:

        Hi Gough,
        Thanks for your reply. The 100 grams was the weight of the whole unit, so it seems the battery is no more than 3000 mAh.
        Hopefully I will get all my money back. If I add another similar battery in parallel to make it double capacity would that be OK and would I need to have a matched pair as in capacity and age?
        At the moment I have a phone with removable batteries and I have several which I charge up and keep handy so I really don’t need this device but I know people who have iphones and I was seeing if this would be good for them. It seems not. I can’t understand why all phones don’t have removable batteries as it seems logical.
        Anyway thanks for your information.
        Kind Regards.

        • lui_gough says:

          I don’t think it’s a wise idea to parallel cells unless they come from the same batch, same manufacturer, same age, and same condition. Otherwise, it is entirely possible that cell mismatches may accelerate the death of one cell over the other, and depending on the mode of failure, it may jeopardize the safety of the whole unit as it could cause the still-working cell to dump its charge into the failed cell.

          I would agree that removable cells make a great idea, but it also opens up liabilities for companies. Part of it is the constant “phone exploded and almost killed me” maneuver which many seem to pull to get some publicity, or a new phone. Fake low-quality cells exist – for example, refer to my challenges in getting a genuine Samsung Galaxy SIII replacement battery (all claimed to be genuine, and aftermarket cells may be a quality/safety issue too).
          http://goughlui.com/?p=6887
          http://goughlui.com/?p=6908
          http://goughlui.com/?p=7044
          http://goughlui.com/?p=8494

          I suppose that it’s always possible for experienced or ambitious end users to replace internal cells themselves at the end-of-life but I think the inbuilt obsolescence is deliberate and a method of ensuring repeat business.

          However, I do agree that the option should be there for the end user to decide!. It would go to saving so much waste and frustration for all.

          – Gough

  20. G. McGill says:

    Just a suggestion. Wouldn’t it be easier to just order one of these packs, disassemble it – and remove all the cells.

    Then load them into a La Crosse smart battery charger and set it to Test or Refresh – and then it would run a couple of deplete/charge cycles – and then show you the exact capacity of each cell.

    Considering the chargers can be found for $40 on Amazon it might be a good way to do it.

    Good read though, thanks!

    • lui_gough says:

      Unfortunately, I don’t have confidence in the accuracy of charger in terms of how repeatable the results are, as it isn’t designed for accuracy, whereas on the other hand, the multimeter based solution I have has a basic accuracy of 0.012%. The other thing is that the power bank performance is also due to the way the PCB manages the power – how well the charger terminates the charge, how efficent the boost converter is at
      converting the charge. Testing in this manner shows the effective capacity a user can expect, which is more relevant.

      However, if someone wants to harvest the cells for other uses, then maybe that could be a test worth doing.

      – Gough

    • lui_gough says:

      Another thing I realized during some research – it doesn’t seem La Crosse make a unit for Lithium-Ion chemistry, do they? The Ni-MH units for AA aren’t suitable for testing this kind of battery.

      – Gough

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