If you have ever shopped for or even seen a branded power bank in a store orMachine to test battery capacity (mAh) online, you have probably noticed that, in many cases, the mAh is written in the largest letters on the front of the package or in the most prominent position on the product page . But how many people actually know what mAh is and how it should influence your purchasing decision?

mAh stands for milliampere hour. It is used to describe the capacity of the battery or how much charge the battery will hold. The higher the mAh the more charge the battery holds. The more charge that can be stored in the power bank the more charge can transfer to other devices.

When picking out a promotional power bank you should make sure that there is enough capacity to charge any device that you might charge with it. You can check our table for battery capacity on common smartphones and tablets (final question on this faq page). Let us pick the iPhone 7 as an example. Although the battery specs are not listed on Apples’ website, nor could anyone at their customer service number tell me the battery capacity, there are several other websites that I found that all seem to agree that the battery is 1,960 mAh.  Thus, to fully charge the iPhone 7, we would recommend a power bank with at least 2,100 mAh. The Samsung Galaxy Tab S2 with a 9.7” display has a 7,870 mAh battery. To fully charge this tablet we would recommend a power bank with at least 8,100 mAh.

You probably noticed that the power banks that I recommended for each example have a capacity that is slightly higher than that of the sample devices. This is because a small percentage of the energy that is stored in the power bank is used to transfer said energy to the battery in your device.  A fully charged 2,200 mAh power bank will not fully charge a completely depleted phone with a 2,200 mAh battery. It should get it to somewhere in the 90-95% range.

Another item to keep in mind is that for a power bank to charge a battery from 10% to 85% will take a, relatively, much shorter amount of time than to take it from 85% to 100%. It will also use a, relatively, larger percentage of the power bank’s charge.  The best way that I have seen to explain this is something that I read online a long time ago. (You will have to pardon me for not remembering where/from whom I got the example.) If I know that these 100 items will fit into this backpack with no space for anything else, I can quite easily throw 85 or 90 of these items in. However, it is the last 10 or so that I have to spend extra time making certain the first ones are packed neatly so that I can fit these last ones in. It works the same way with the power banks, it can dump most of the charge in quickly, but to get it the final bit, will take longer and is less efficient.

One final note: A common misconception is that the more mAh a power bank has, the quicker it will charge your device. This is not true. The output current is what determines this, but this is a discussion for another time.

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