What Are Portable Power Banks?

  • 3 min read
Let’s get right to it. If there aren’t any outlets to plug into, what do you rely on for power? How do you charge the device you have and plan on continuing to use? The answer to that question is quite simple and is an increasingly popular industry, Portable Power, more specifically, Portable Power Banks.

If you want to stay powered you must be outfitted with a reliable source of reserve power that comes in a compact and easy to carry package. We are going to go over the most frequently asked questions and explain what portable power banks are.

What Are Portable Power Banks?

If you want to make an informed purchase, the best practice is to understand the basic terminology. A portable power bank is a battery which resides in a special case that has a specific circuit that controls power flow.

Much like a bank account where you deposit you hard earned cash and withdraw it later, a power bank allows you to store electrical energy and then use it later to charge your device. Before we get into what types of power banks there are, let's understand the power that is stored within these units.

What Does mAh Stand for?

While these units come in all shapes and sizes, they also vary in power capacity, much like the variety of smartphones on the market.

The term you most often seen while researching these units is mAh. It’s an abbreviation for “milliampere hour,” and it’s a way to express the electrical capacity of smaller batteries. The A is capitalized because, under the International System of Units, “ampere” is always represented with a capital A. To put it simply, the mAh rating denotes capacity for power flow over time.

Portable Power Bank mAh recharge table

Now that we know what a power bank is and what the power that resides in them is, let’s take a look at what types of power banks there are.

What Types of Power Banks are There?

While there are various styles and brands that cater to a user’s specific needs, you can break down the types of portable power banks into three categories.

Universal Power Banks

These come in many sizes and configurations that cater to you device requirements. Some may feature both an AC outlet and USB ports plus USB-C, while others may only have a single USB option.

Solar-Charged Power Banks

These have photovoltaic panels which can charge the internal battery of the pack when placed in sunlight.

Battery Case (for your phone)

These typically attach to the back of your phone and, while convenient, they have narrow device compatibility. Portable power banks for your phone are typically smaller in power (mAh) and will only recharge your phone a couple of times before requiring a recharge of its own. Here are some of the top portable power banks according to Android Central.

How Many Times Can a Power Bank Charge my Device?

Here’s a question we see frequently and that can be answered with a formula as shown below.

(Labeled capacity of the power bank x 3.7 / output voltage of power bank) x 0.85 / battery capacity of device =  Total number of recharges.
Now, that you have the formula all let’s try an example.  We can use a 40,200 mAh power supply and an iPhone 8 which has a battery capacity of 1821 mAh.

(40,200 mAh x 3.7 / 5) x 0.85 / 1821 mAH = 13.8 recharges

First we have the labeled capacity for the power bank - 40,200 mAh

Second we multiply that by 3.7. This number is the average voltage you will find in a battery cell. We get this number normally by finding the midpoint between a fully charged cell and an empty cell.

Third step is dividing 148,740  (sum of 40,200 x 3.7) by 5. We divide by 5 because this is the average voltage output of a typical power bank.

We continue on to the fourth step which is multiplying 29,748 (sum of 148,740 / 5) by 0.85, which is the average efficiency of a power bank.

Yes, this means you will never get 100% of the total expected output.

Finally we divide 25,285.8 (the sum of 29,748 x 0.85) by the battery capacity of the desired device you are trying to charge, in this case the iPhone 8 is 1,821 mAh.

The final sum comes out to 13.8 and that is how many times you can recharge an iPhone 8 with a 40,200 mAh portable power supply.


There you have it. You now know what a power bank is, what power (mAh) is stored in a power bank, and how to calculate how many recharges your power bank can supply to whatever device you decide to use.  If you have any questions feel free to leave a comment below and reach out for additional support. Keep an eye out for future posts!