Powerbank Capacity Explained: A Quick Guide

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You have just purchased a highly-rated popular power bank such as Anker PowerCore Slim 10000 PD USB-C or MI 10000 Ultra USB-C and can’t wait to charge your phone multiple times. But after charging a few times, something does not seem to add-up! Power bank users often get mystified with the mismatch between the expected capacity of their purchased power banks and the actual number of charges that they get for their phones or tablets.

We expect to fully charge our iPhone 15/14/13 with about 3000mAh battery a minimum of 3 times using a 10000mAH power bank as 3000 x 3 = 9000. However, in reality, your phone will get fully charged about 2 times!!

A quick rule of thumb is to assume that the real world capacity of your powerbank is 2/3 of the theoretical capacity mentioned on the box. So for a  good 10000 mAH power bank, it will be about 6600 mAH or about 2 full charges for the iPhone 15/14/13 and for a good 26800 mah power bank it will be about 18000 mAH, or about six full charges for the iPhone 15/14/13 or iPhone 15/14/13 Pro.

Usually, you begin charging your phone with the power bank from 20-40% level. So, with bestselling 10000 mAH power bank such as Anker PowerCore 10000 USB-C or MI 10000 Ultra you can expect –

  • Three charges from 20% to 100% for iPhone 15/14/13/12/11, XR, X, XS, XS Max, 8+, 7+ Samsung S23/S22 etc.
  • Two charges  from 20%  to 100% for iPhone 15/14/13/12/11 Pro, Samsung S23, S22, Pixel 8/7  etc.
  • Two charges from 40% to 100% for iPhone 15/14 Pro Max, Samsung S23/S22/S21 Ultra, Pixel 8/7 Pro etc.
  • Five charges from 30% to 100% for iPhone 13/12 mini, SE 2023/20, SE, iPhone 8, 7 etc.
pd portable charger for iPhone XI and XRR
Anker PowerCore 10000 USB-C fast charges iPhone 15/14/13/12/11 from 0 to 60% in 30 mins & charges most Android phones fully two times

Understanding Power Bank Capacity

The reason for this mismatch is that mAH is not a good unit to measure battery capacity when the voltages of the battery and charged devices are different. Li-ion batteries used in power banks output 3.7 volt (nominal) but your phones’ batteries get charged at 5 volt.

mWH or watt-hours is the ideal way to measure a battery’s stored energy as it is voltage-independent and takes into account the total energy of the battery.

So a power bank with 10000 mAH capacity actually has 10000 mAH capacity at 3.7 volt. Total energy in such a battery in mWH will be 10000 mah x 3.7 volt = 37000 mWH.

When the output is at 5 volt, the Mah capacity of this battery will be lower. The capacity of  the battery while charging at 5 volt output will be 37000 mWH divided by 5V or 7400 mAH.

In addition to this, energy is also lost during the conversion process from 3.7 to 5 volt, due to the resistance of the connecting cable, and during the charging process. You may have noticed that the phones often get warm and mildly hot during charging. This is simply electrical energy getting wasted as heat during the charging process and is unavoidable in any charging process.

Fast-charging further wastes energy as it is usually done at much higher voltages (12 or 9 volts) when the battery is less than 50-60%.

Many other factors, such as ambient temperature and the exact chemistry of the powerbank and smartphone batteries also determine the real charging performance of the powerbank. Assuming a 10% loss (or 90% efficiency), this leads to an effective capacity of 7400 x .90 = 6660 mAH . This is approximately 2/3 of the on-paper or advertised 10000 mAH capacity of the powerbank.

As the actual charging performance may vary from device to device, you can roughly assume the 2/3 capacity number to calculate how many times your smartphone will get charged by your powerbank.

For example, a quality 26800 mAH powerbank such as Anker PowerCore+ 26800  will have a real world capacity of 26800/.66 = About 18,000 mAH. Hence, it will charge an Apple iPhone 13/12 (2815 mAH battery) about 18000 / 2815= about 6 times! It will charge the iPhone 15/14/13/12 Pro/iPhone 15/14/13/12/11, or Samsung S24/S23 about 18000 / 3400 or about 5+ times.

Similarly, a good 20,000 mAH power bank such as Anker PowerCore Essential 20000 USB-C PD will charge iPhone 13/12 about five times and Samsung S24/S23, A55/A54 nearly 4 times. A quality 10000 mAH powerbank such as MI 10000 Ultra USB-C will charge iPhone 13/12 from 30% to 100% about three times.

Here are some tips to maximize the power capacity of your power banks.

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How to Maximise Power Bank Capacity

To extract maximum power from your powerbank follow the following tips –

Do not use USB-C Fast Charging or QuickCharge Ports often

Most modern phones ship with fast charging technologies such as QuickCharge 3.0 or USB-C PD based fast charge. Such fast charging will charge your phone at extremely fast speeds using higher voltages or larger currents than normal. For example, Apple iPhone 15/14/13/12, 11, 11 Pro, XR, XS/XS Max,  X/8/8+, SE 2020 can get charged from zero to 60% in about 30 minutes with USB-C PD fast charging power banks such as the Anker PowerCore Slim 10000 PD power bank using a USB-C to Lightning cable.

Best Power Banks for Samsung Galaxy S10, S10+, S10e, S9, S9+, Note 10, Note 9, & S8, S8+

Fast charging is great when you are in hurry. However, fast charging uses high voltages (9 volt or 12 volt) and this further reduces the usable battery capacity of the powerbank and drains power bank battery much faster.

Using standard 2 amp or even 1 amp ports on the powerbank will make your powerbank give as much as 20% extra charging capacity.

High capacity power bank
Anker Powercore+ 26800 can charge iPhone 13/12/XR/11 almost seven times! It has a QuickCharge 3.0 port (green) and 2 regular ports. Use regular ports to maximise power bank capacity and QC port when charging in a hurry 

Use Good Quality Power Banks

Quality power banks have higher efficiency of up to 95% due to optimized circuits. Such power banks can better fine-tune voltage and reduce power wasted due to heat.

Use Quality Short Cables

Quality short cables have lower resistance as they use copper and premium metal contacts and hence lead to less loss of power.

Use 1 Amp or 2 Amp Regular USB Charging ports if not in a hurry

Charging via non-fast-charging 1 Amp or 2 Amp/2.1 Amp regular USB ports will ensure greater efficiency than charging at fast-charging high current Quickcharge USB ports as more power is wasted at higher voltages and currents.

Best USB-C Portable Chargers

Best Portable Chargers & Power Banks 2023

25 thoughts on “Powerbank Capacity Explained: A Quick Guide

  1. I will be needing a powerbank to charge an iphone X and 8 while back packing for 7 days. Was looking into solar options (I also have goal zero panels already), but it seems impractical to rely on solar for recharging and a better approach seems to just bring a fully charged powerbank that will last the week.

    should I get a 10,000mah powerbank or 20,000mah one? (We’d mainly just be using for taking photos). If my son has his own power bank, would the 10,000mah be enough? was looking at an Anker one as well as a Skullcandy 10,000 from REI. Do you have a recommendation for a good powerbank that would also be compatible with my goal zero panels in case I use them in the future?


    1. Hi,
      I recommended at least one 20000 mAH power bank as you have two slightly old phones and the extra capacity gives a lot of buffer while travelling with multiple phones. Ideally, for long trips and multiple phones – two power banks give a lot of flexibility without the hassle, unpredictability and weight of slow solar charging –
      – One 20,000 power bank as “base” to be kept in backpack.
      – Second 10,000 mah power bank for carrying on person/pocket and on-the-go charging.
      For 20,000 mah, EasyAcc 20000 offers terrific solar compatibility and is excellent as a no frills “base” power bank.
      For 10000 mah, any slim and light fast-charging power bank – such as Anker PowerCore Slim 10000 or ZMI 10000 USB-C will be excellent for easy pocket/hand carry and quick charging on the move.

      If your travel-partner has a 10,000 mah power bank, then one 20000 mah power bank should be adequate.

  2. Hi,
    I just bought a brand new Xiaomi power bank 3 Fast Charging version with 10000mAh. I noticed that the rated capacity is showing only 5500mAh. Seems very less to me.
    What is the best rated capacity suppose to have in a 10000 mAh power bank? Also i noticed that in the packaging the manufacturing date was Dec 2019, there is like 1 year ago. Will that impact or degrade the charging performance since it might be sitting in the shelf for a year?


    1. Hi Max, One year is on the higher side for storage of power banks and if the power bank was originally stored depleted, it may almost render it useless. However, if the power bank was stored at near half-charge (50%), most good quality modern power banks such as original Mi power banks will be fine after one year. We will suggest to check its battery status on opening the package, if the battery status is around 50% then the power bank is OK, otherwise it is best to get a replacement. Rated capacity of 5500 mAH (rated at 5.1v@2.6 amp for Mi Power Bank 3) in a 10000mAH nominal advertised capacity power bank is fine and normal.

  3. Hie, l need advise on whether to purchase a 10000mah redmi powerbank for a p30 lite which unfortunately supports 10watts fast charge whereas my phone is an 18 watt fast charging phone OR l should just buy a 20000mah power bank which is more expensive?

    1. Hi Gugue, The Redmi 10000 power bank will work perfectly fine with your Huawei P30 Lite and charge it at a decent 10-watt speed (20% to 80% in 1 hr). With 18 watt, you will get from 20% to 80% in about 40 mins. You do not need a twice as heavy and twice as expensive 20K power bank if you are OK with charging taking 15-20 mins more. A lighter power bank is easier to carry around and use frequently, so a 10000mAh power bank is perfectly fine!

  4. I purchased a 10,000mAh USB-C Power Bank. I have no idea how it works. The box had no instructions. Do I have to charge it before it will charge my phone? It is heavy and I don’t like that. Any help will be appreciated. Thank you.

    1. Hi, Yes, You will have to charge the power bank before using it as it usually gets discharged during storage in warehouses etc. With one charge it will give you about 3 charges for iPhone 8/7 etc.

      A 10000mah powerbank should not weigh more than about 8 oz max (~250 grams) these days. If it weighs more, it means that it is old or probably of poor quality. Please do let us know more about your phone and power bank brand and model so we can guide you further!

  5. Hi,
    I’m looking for a recommendation of a Power Bank, travel friendly to fit in my little bag hence to be light.
    To be able charge the following:
    – Samsung S8+
    – iPod Pro
    – Laptop Lenovo ThinkBook
    Not necessary all at once but certainly to be able to charge them if they need be.
    Other requirements I would love to have around 26000mAh as I am aware that is going to have a smaller net capacity.
    If it’s going to be wireless that will be a nice bonus at the reasonable price of course.

    I did some research but looks like I couldn’t find something yet with all my boxes ticked.
    Thank you in advance for your support.

      1. Hi,
        The laptop I purchased only 2 months ago, model Lenovo ThinkBook 15 Core i7 16GB 512GB SSD 15.6″ Win10 Pro Laptop.
        The Ipod bought in 2018

        I forgot to mention that I want the Power Bank to be fast charging too on top of good capacity, slim, light and compatible with my items.

        Thank you,

      2. Thank you for your message.
        Lenovo ThinkBook 15 Core i7 16GB 512GB SSD 15.6″ Win10 Pro Laptop I purchased only couple of months ago.
        iPad Pro A9X, iOS, 9.7″, Wi-Fi, 128GB 2016 although I though I purchased in 2018
        I would also want to be able to charge Samsung EarBuds. I forgot to mention that I want the Power Bank to be fast charging too on top of good capacity, slim, light and compatible with my items.
        Kindest regards,

        1. Hi Liliana,
          Apologies for the delayed reply as I had to verify/double-check some charging specifics for your devices. Thinkbook 15 comes with a 65-watt charger and the good news is that it can be also charged via the USB-C port. This increases our options. S8+ also fast-charges over USB-C PD. For your specific requirements, we recommend either of these three 60-watt USB-C PD powerbanks –

          • Anker PowerCore III Elite 25600 This has near maximum TSA-allowed capacity, weighs 1.3 lb (about 600gm) and comes with a 65 watt USB-C charger that can also replace your laptop’s adapter if required (as well as S8+ adapter if needed). It can fast charge all your three devices and also charge three devices (Thinkbook/iPad Pro 2016/S8+) at the same time. It will also charge your Samsung Earbuds in trickle power mode. With 60-watt max PD output, it can fast-charge the Thinkbook (as well as S8+ and iPad) at its max charging speed.
          • ZMI Powerpack Pro 20000. This is the lightest, slimmest and most compact of the three (just 15oz/440 grams) It also has all the features of the Anker PowerCore Elite III including trickle-charge mode but offers 80% of its capacity. Combined with an ZMI 65-watt PD adapter, it will cost much less and have enough power to charge your Thinkbook half once, your iPad half once and the S8+ from 20% to 100% once.
          • Omni Mobile 25600 – Our last choice (due to its 1.7 lb/770 gram weight). This powerbank has all the features of the Anker PowerCore Elite but has one extra feature – wireless charging. It however weighs about 100gm/3.5oz s more than PowerCore Elite III and you will also need a USB-C adapter for it. Even with an extra USB-C adapter (we recommend ZMI 65-watt PD adapter), It will cost lower than the Anker and offer wireless charging, though at the cost of extra weight. Omni Mobile 25600 is also the only powerbank of the three to offer passthrough-charging. This means you can charge your S8+ and the iPad while charging the power bank from the USB-C port.

          Thanks! and please feel free to send any further queries.

          1. Hi there,
            I cannot be more grateful for your time and suggestions. I looked up for all those 3 suggestions and looks like they are in U.S. I forgot to mentioned that I am in the UK.
            The last one I found to be the most expensive out of all of them unless I’m looking at the wrong item. However, it is most likely to buy this one before I will go traveling as it fits all the boxes apart from the weight and price.

            For the time being I have to get a very light power bank, just for the mobile phone to fit in my daily tiny bag in case my battery is running low. I use to get low battery after taking lots of pictures and video recordings. For this particular case, I have been recommended Samsung 10000mAh wireless. What is your thought?

          2. Hi Liliana,
            OmniMobile 25600 is indeed priced very steeply in the UK (almost double that of US). However, the price often drops by about 50 GBP and one can track the price to get a better deal.
            Samsung 10000 wireless is an excellent wireless power bank for S8+ and it is also one of our recommended best wireless power banks for Samsung phones. Please note that there are two different models of Samsung 10000 Wireless available in the market. Samsung recently released an upgraded model of the 10000mah wireless powerbank for newer Samsung phones – the Samsung 10000 Wireless 25-watt version(UK Link).

            The newer model has two USB-C ports (older one has a USB regular and a USB-C), supports USB-C PD, and can fast-charge Note 20/10, S20 etc. at 25-watts while older one charged at max 15-watts and did not support USB-C PD. Both will however charge the S8+ at same speed of 15-watts as S8+ supports a maximum of 15-watt fast-charging.

            For your current devices – S8+, earbuds & the iPad Pro, – the older Samsung 10000 Wireless UK Link is a great option as it has regular USB port for charging iPad 2016 and is available currently at a very reasonable price as well.

            If, however, you require future-proof compatibility for newer Samsung phones (and latest iPads/iPad Pros/iPhones that support USB-C PD charging), then the newer Samsung 10000 Wireless UK Link is a better choice, though for a higher price. Also, you will need a USB-C to Lightning cable for charging the iPad 2016 as it lacks a regular USB port.


    1. I have a 10000mAh power bank and when I open it, I found out that all 3 batteries inside are already defective and I want to replace it. Each battery has a 2200 mAh 3.7 V label (Lith-ion 18650 battery). Can I replace the batteries with 3000 mAh 3.7 V?

      Note: The board seems fine and still working,only the batteries are damage

      1. Hi Abel, Yes you can replace 2000mAH 3.7v Li-ion 18650 batteries with 3000 mAH or higher 3.7v 18650 Li-ion batteries. Charging circuits are tuned to voltages and battery-chemistry and hence replacing with higher capacity similar type batteries does not cause any problems.

  6. Hi, I am looking at solar battery banks – average 20000 to 25000mah seems good. Seen one that is rated as 300,000mah here in Australia. Thought it was a typo but it isn’t. How can this be. Many thanx .

    1. Hi Don, We do not recommend any solar powerbanks as these are not practical in practice. The tiny solar panel on top of the solar power banks is not sufficient to charge powerbank to any decent extent in a day of sunlight. It is always better to get a good regular powerbank and charge it with a separate minimum 15-watt solar panel. (Link for Australia)
      The few 300,000mAH solar power banks available on Ebay/Amazon AU are indeed typos as no way can a portable power bank hold that much battery without weighing 10kgs!

  7. Hi I’ve a i26s solar 26800 power bank.
    It’ll change all my devices apart from my iPhone 8.
    Any ideas why please?

    Thank you

    1. Unfortunately, Nearly all solar powerbanks available at present are of hit or miss quality. Usually these are clones of each other with different names. We do not recommend any solar powerbanks for this reason, even though they seem very tempting. We suggest you try different ports as often some ports work with some phones and some do not. Also try different combinations of plugging in cable in phone after plugging it in powerbank or plugging cable in phone before plugging in phone etc. Sometimes this works.

  8. I want to compare the PD Pioneer 26800mAh Portable Charger Model: RP-PB058 and the PD Pioneer 20000mAh 60W Portable Charger 2-Port Power Bank. I know the difference in the capacity as to 20,000 vs 26,800 but can you explain why I might want 30W vs 60W. I want to charge Apple iPhone, iPad and MacBook Pro, separately. thanks

    1. Hi David, Consider power banks as similar to water-tanks, then maH (or WH) numbers will be gallons/liters and watts will be rate of flow of water. To simplify a bit, you can say that watts is the size/width of the water-outlet of the tank. The bigger the size of the outlet pipe (more watts), the more quickly you can fill (charge) the buckets (phones, iPads or laptops).

      For your specific requirements, we recommend 45-watt or 60-watt power banks as Macbook Pros can handle quite a lot of input power and 60-65 watt powerbanks will MB Pro twice as faster as 30-watt powerbank. also 60-watt will allow you to charge phone and Macbook at same time at faster speed.

  9. I am SO confused. I will be hiking in the mountains of Peru for 8 days with a iPhone 11 pro max and a Autel Evo 2 drone (each battery is Rated Capacity: 7100 mHh, 82 Wh, Normal Voltage: 11.55V, Max charge voltage: 13.20V and the charger for it is Input:100-240v, 50/60Hz, 1.5A Output: 13.2V with a bunch other numbers then it say Total Output Power: 66W Max)

    I haven’t the foggiest idea of what I need/should take. The mules will carry some of our stuff and then I’ll be carrying my drone, some batteries, my water etc in my backpack. What should I get for a PowerBank and recharger for it???? Someone PLEASE help me. I leave June 22nd. I need to figure this out!

    1. Hi Christen, At minimum you will need a good solar charger and at least two solar-compatible powerbanks. If you plan to charge the drone in the wild, then at least one of the power banks should have adjustable DC voltage output (or AC outlet) for charging the drone at 12-volt or via the drone’s AC adapter . We recommend
      Omnicharge 20+ powerbank – It is solar compatible, has an adjustable voltage DC outlet, and also an AC adapter with up to 100w output. It also supports passthrough charging so you can charge stuff while charging the powerbank (Very important when solar charging). This is best used for charging the drone through the AC outlet. It should charge the Autel Evo II’s 7100 mah battery about 80% on one full charge. Evo II’s battery charges at high-voltage (12-13 volt). So, basically a normal 20000 mah/5v power bank and 7100mah/12-13V Autel battery will have nearly same power. After accounting for AC/DC loss you should get about 75-80% battery for EVo II battery-pack. Best strategy is to first use solar panel to charge Omnicharge and then later use Omnicharge to charge drone battery. Avoid pass-through charging of drone unless it is absolutely urgent.
      EasyACC 26000 powerbank. It is a rock-solid no-frills solar compatible high-capacity powerbank. This has been chosen solely for solar compatibility and pass-through solar charging support. Even though it does not have fast-charging for iPhone etc., that is not an issue as one should anyway not fast-charge the phone from power-bank in the wild as it wastes precious battery.
      Anker 21-watt foldable Weather-resistant Solar panel. It can charge both your powerbanks and also charge your phone directly.
      – A good 45-watt PD charger for charging the Omnicharge in 3 hrs and the Easyacc Powerbank at fast-speed in 10 hrs.


      -Avoid PD-fast-charging the iPhone 11 Pro Max from the powerbank’s USB-C port when away from civilization as it needs more power for same amount of charge. Ideally, charge from the regular USB ports.
      -For same reason, avoid wireless charging the 11 Pro Max when off-the-grid or on low-battery. Omnicharge Omni 20+ has an inbuilt wireless charger. It is very handy but consumes more power for same amount of charge.
      Feel free to send any further queries.


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