Your power bank’s true capacity

Are you wondering why your 4,000mAh power bank can’t fully charge your iPhone 8 with a 1821mAh battery twice? In theory, it should work, right?

The capacity of batteries is usually referred to as milliampere-hours (abbreviated mAh). One could therefore think that 4000mAh will then correspond to 4000 transferred mAh to a mobile phone. But unfortunately, it is not that simple. Let me explain why.

The truth about your power bank​

The truth is that your power bank requires energy to drive its circuits that monitor the charge. But some are also wasted to change the voltage from their battery to match your mobile phone’s requirements. This voltage, which is the difference between the batteries, is deliberately converted into heat via a volt regulator or similar component. It is therefore often said that, for safety’s sake, 25-30% of the power bank’s battery capacity should be deducted. Of course, there are many differences between different models. But in this way, you can be sure that the product you buy lives up to expectations.

By using the following formula, you can calculate the lowest capacity you need to be able to charge your mobile phone once. Mobile phone battery / 0.7 = power bank requirement. Simple, right? Keep this 25 – 30 % in mind the next time you buy a power bank, to be on the safe side. Then you can avoid these unwelcome surprises when you can only charge the phone 2 of the maybe 3-4 promised times. Of course, there are manufacturers who are more accurate with the performance of their products. But that it is difficult to determine. So do not take a chance.

Power bank capacity in numbers

Below you can see a rough estimate of the number of charges versus the unit’s capacity. But also keep in mind that if the phone is switched on or used during charging, this also affects how much you get out of the battery.

mAh Fully charged phones (approximately)
2600
0-1
3000
0-1
5000
1-2
10000
2-4
12000
3-5

Summary

Make sure to buy your next power bank from a trusted brand. We also recommend that you use the data table above to calculate how many mAh you really need for all your tech during your adventures. And if you need the unit to keep your phone charges for pictures, make sure to check out our 11 tips and tricks for better outdoor photos.

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Cover by: Fridh, Andreas. Power bank. 2019.
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