Powerbank Capacity Explained: A Quick Guide

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Best power bank for Oneplus 7T Pro
Aukey 10000 USB-C fully charges latest iPhone 11/11 Pro/XR/X/8/8+ & most Android phones two times, and iPhone 8/7/6s/6/SE/5s three times. It can be charged via USB-C or micro-USB port

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 charge our 2000 mAH battery smartphone 5 times using a 10000mAH power bank as 2000 x 5 =10000. However, in reality, your phone will get charged about 3 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 quality 10000 mAH powerbank, it will be about 6600 mAH or about 3 and a half charges for the iPhone 8 and for a good quality 26000 mah power bank it will be about 18000 mAH, or about 10 charges for the iPhone 8.

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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.

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 8 (1820 mAH battery) about 18000 / 1820 = about 10 times! It will charge the iPhone 11, or Samsung S9 about 18000 / 3400 or about 5+ times.

Similarly, a good 20,000 mAH power bank such as Aukey 20100 Lightning Input + USB C PD or Anker PowerCore Essential 20000 USB-C  PD will charge iPhone 8 about seven times and Samsung S10 about 4 times. A quality 10000 mAH powerbank such as EasyAcc Brilliant 10000 will charge iPhone 8 nearly four times.

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

Best Portable Chargers for iPhone 11, 11 Pro/Max, XR, XS Max, XS, X, 8 Plus, 8 & More

Maximising Power Bank Capacity

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

Use Fast Charging or QuickCharge Ports Only When required

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 11, 11 Pro, XR, XS/XS Max,  X/8/8+, SE 2020 can get charged from zero to 50% in 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. Quickcharge 3.0 phones such as LG G8, G7 or V40, V30 can get charged from zero to 80% in 35 minutes using QuickCharge 3.0.

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 8 almost 10 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 Power Banks : Best Power Delivery (PD) Portable Chargers

Best Portable Chargers & Power Banks August 2020

8 thoughts on “Powerbank Capacity Explained: A Quick Guide

  1. 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!

  2. 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.

  3. 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.

  4. 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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