4 Tips to Buying Power Banks

With technology progressing and evolving at such a rapid rate, choosing the right power bank for your needs can be a very daunting task. There are so many manufactures, shapes, designs and capacities that it could be a little be overwhelming to find a reliable source to point you in the right direction.

In order to break this down into simple calculations, one has to first decide on the devices that are intended to be supported. To illustrate this, in this post I want to use standard and plus size mobile phones and some basic tablet models namely those from Apple, Samsung and Sony. I have owned devices from these manufacturers and have been faced with this question of how big the power bank needs to be to keep these devices operational.

This is a logical question since the power bank intended for 1 mobile phone will be substantially smaller than one intended to keep 2 phones charged or a phone/tablet combination. The storage capacity and combination should be clearly defined before purchasing a power bank unit.

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General Sizing Rules:

If you were to ask someone what the battery capacity of their phone is, most people would have no idea. I recently purchased a Samsung S9 Plus and the battery capacity differed substantially from the IPhone 6s that I had before. In order to adequately size a power bank, the general rule is that the power bank should be approx. 4 times the capacity of the battery you wish to recharge.

This 4 factor size rule is a rough guideline that enables the unit, at an absolute minimum, to provide enough power for 2 full battery recharges and will also cover natural power losses resulting from increased temperatures, cable losses and so on. There will be power left over after the 2 full charges and this can be used to top up in emergency situations.

In the case of tablets, the larger on-board battery capacity makes a 4 factor a little unrealistic and a factor of 2 is more practical. This will provide one full charge with a little left over to spare. The second reason of choosing a factor of 2 is that typical power-banks currently on offer, rarely exceed the 25,000 mAh range which would then place the requirements of a 4 factor rating well above what is currently on offer.

Current Requirements:

Current requirements differ between the models and this can be illustrated the most mobile phones require as little as 0.5A which can be supplied by a normal USB 1 port whereas most tablet devices require a minimum current of 1A of current to start charging but this can be as much as 2.1A for some models.

It must be said that it will take a long time to charge if the current is on the minimum supply amount therefore supplying sufficient amount of power will be increase the charging efficiency of the unit.

Brands & Power Bank Calculations:

Standard Mobile Phones:

Manufacturer Model Battery Capacity Factor Power Pack Size
Apple IPhone 8 1,825 mAh 4 ≥7,300 mAh
Samsung Galaxy S9 3,000 mAh 4 ≥12,000 mAh
Sony Xperia XZ 2,900 mAh 4 ≥11,600 mAh

Plus Sized Mobile Phones:

Manufacturer Model Battery Capacity Factor Power Pack Size
Apple IPhone 8 Plus 2,675 mAh 4 ≥10,700 mAh
Samsung Galaxy S9 Plus 3,500 mAh 4 ≥14,000 mAh
Sony Xperia XZ Premium 3,230 mAh 4 ≥12,920 mAh


Manufacturer Model Battery Capacity Factor Power Pack Size
Apple IPad 2 6,930 mAh 2 ≥ 13,860 mAh
Samsung Galaxy Tablet 7,300 mAh 2 ≥ 14,600 mAh
Sony Xperia Z4 6,000 mAh 2 ≥ 12,000 mAh

Every person is different in that they have different combinations of mobile devices with differing power requirements so for me, I have a Samsung S9 Plus and a Samsung Galaxy Tablet and that’s the one I will illustrate how to calculate the appropriate power bank.

With above-mentioned combination, I have 2 options available to me. Either I can purchase one large power bank to support both devices or I can purchase 2 separate units that will together give me the correct power availability.

Option 1 – One Power Bank:

On the chart the power requirements for my Phone and Tablet are 14,000mAh and 14,600mAh respectively which results in a combined total of 28,600mAh of required power support. This is a large amount and taking into account the market offering limitations, a unit of 24,000mAh – 25,000mAh will provide 2 full charges for the phone and one full charge for the tablet.

It must be said at this point, it is highly unlikely that someone will need much more than this during normal usage. If the situation does occur that this is not enough power, the frequency will be very low and this shouldn’t be cause for concern.

Option 2 – Two Power Banks:

Taking the example from above, I would require 2 power-banks of approx. 14,000mAh each to provide enough power for these 2 electronics.

Brand Recommendations

There are so many brands on offer that it could be very difficult to know which ones are reputable and which ones will actually do what they say they will. Here I provide you with my top 5 units that will provide good support without breaking the bank:

1. Anker PowerCore:

  • Power Delivery Range: 5,000 mAh – 26,800 mAh
  • Price: $15 – $50
  • Customer Rating: 4.5 Stars
  • Customer Reviews: ≥ 6.500 reviews

2. Aikove Power Bank:

  • Power Delivery Range: 24,000 mAh
  • Price: $30
  • Customer Rating: 4 Stars
  • Customer Reviews: ≥ 160 reviews

3. SiKER Power Banks:

  • Power Delivery Range: 20,000 mAh
  • Price: $18
  • Customer Rating: 4.5 Stars
  • Customer Reviews: ≥120 reviews

4. Pilot X7:

  • Power Delivery Range: 20,000 mAh
  • Price: $25
  • Customer Rating: 4 Stars
  • Customer Reviews: ≥ 1,053 reviews

5. RAVPower

  • Power Delivery Range: 22,000 mAh
  • Price: $30
  • Customer Rating: 4.5 Stars
  • Customer Reviews: ≥ 180 reviews

In the world of electronics, it is always advisable to have too much rather than too little. It is easier to scale back based on too much capacity than to invest in something that shortly proves inadequate for your needs.

Should you have further questions leave me a text in the comments section and I will do my best to get back to you as soon as possible.

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2 Responses

  1. Jeff says:

    My wife and each have a smart phone and laptops but I do not know what a power bank is and why I might need one. Are there some basic situations that point to the need for a power bank?
    Also, how would I find the battery capacity specs for each of my devices?

    • Richard says:

      Hello Jeff,

      The principle of a Power Bank is to serve as a replacement power source to recharge your device when a wall based power sources are not available. The laptop power banks will be slightly different in that they will need to be up-sized for the increase power requirement and are not covered in this article.

      The user manual that is supplied with your smart phone will have a specifications section detailing your on-board battery capacity and failing that, google the make and model with a specific search aimed at battery capacity. Once you have that then follow the steps as described in the article and you have your power bank size requirement. 

      If these provide too much capacity, one can also double the capacity listed in the user manual and this will be large enough for a single charge. 

      Thanks for the comment and should you have other questions then let me know.


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