How do you choose a power bank with the right capacity?

Want to know how often you can charge your smartphone with a 5000mAh power bank? Check how high the actual capacity is. It's 2/3 of 5000mAh, which is about 3330mAh. For example, you can fully charge the 3150mAh battery of the iPhone Air. Large models like the iPhone 17 Pro Max (5100mAh) don't charge all the way. You can charge Android smartphones like the Samsung Galaxy S26 and S26 Ultra (4000 to 5000mAh) for about 65 to 80%. This power bank is ideal for on the go, as it fits in your pocket or bag.

With a 10,000mAh power bank (actual capacity: 6660mAh), you can charge most smartphones once or twice. The size of a smartphone battery differs per device. Many iPhone models have a battery of about 3500mAh, while other devices like the Galaxy S26 Ultra run up to 500mAh. Make sure to check how large your battery is. A 10,000mAh power bank is compact enough for in your pant pocket and suitable for a day out. Do you want to charge other devices in addition to your smartphone, such as earbuds, an e-reader, or a second smartphone? Choose a power bank with a capacity of at least 15,000mAh.

For laptops and tablets, you should choose a power bank with at least a 20,000mAh capacity. Tablet batteries have a capacity between 6000mAh (iPad mini) and 11,000mAh (iPad Pro). With a 20,000mAh power bank (actual capacity: 13,300mAh), you can charge your tablets and laptops at least 1 time. You can even charge small tablets 2 times. For a small laptop like a Chromebook, you need at least 45W power. For large laptops, like a 14 or 16-inch MacBook Pro, you need a 27,000mAh power bank.

With a large 27,000mAh power bank (actual capacity: 18,000mAh), you can charge multiple devices. That's useful if you want to charge your laptop, work smartphone, and private device. You need 60 to 65W power for laptops, and even 100 to 140W for advanced models like a gaming laptop. These large power banks always have multiple USB ports. That means you can charge your devices at the same time. If you only want to charge your smartphone, you can do that 4 to 6 times. That way, you can charge your device every day during a weekend of camping or a festival. Good to know: 27,000mAh is the maximum capacity that you can take on an airplane without permission.

How quickly your power bank can charge your phone, depends on the power in watt (W). All new iPhone models support fast charging via USB-C Power Delivery. With a power bank that charges with a speed of 20W or more, your iPhone is charged for 50% in half an hour. Do you have a Samsung Galaxy S25 or S26? You can charge the fastest with Super Fast Charging. The Samsung Galaxy S26 Ultra even gets 75% battery in half an hour with a power bank with a charging speed of 60W or more.

Do you have an iPhone from the iPhone 12 or an Android device with a magnetic cover? You can charge wirelessly with a MagSafe or Qi2 power bank. These magnetically attach to the back of your phone. That's useful, as you won't need a cable. Newer devices like the iPhone 17 or Samsung Galaxy S26 Ultra charge wirelessly with 25W via Qi 2.2. Keep in mind that wireless charging is a bit slower than with a cable.

The technical side of it is complicated, but the rule is simple. The actual capacity of a power bank is about 2/3 of the capacity indicated. The rest disappears due to voltage conversion or is lost during charging, especially as heat. This means that power banks with a 10,000 or 20,000mAh battery actually have a capacity of only 6660 or 13,330mAh. With modern power banks with USB-C Power Delivery like the latest BlueBuilt models, this loss is smaller.