How do you choose a power bank with the right capacity?
1/3 of the capacity is lost
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 during power conversion or is lost during charging, especially as heat. This means power banks with a battery of 10,000mAh or 20,000mAh actually have a capacity of only 6,660mAh or 13,330mAh. This rule applies to high-quality power banks alone. Budget power banks from cheap wholesalers are even less efficient, so they lose even more energy.
Smartphones: a power bank with 10,000mAh
With a 10,000mAh power bank (actual capacity: 6,660mAh), you can charge most new smartphones about 1.5 times. The size of a smartphone battery differs per device. While 2-year-old smartphones sometimes still have a 2000mAh battery, new devices have a 4000mAh battery. Make sure you check how large your battery is. 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.
Tablets and laptops: a power bank with 20,000mAh
Choose a power bank with a minimum capacity of 20,000mAh for laptops and tablets. Batteries of tablets are between 6,000mAh (iPad Mini) and 10,000mAh (iPad Pro). The average is around 8,000mAh, which also goes for laptops. With a 20,000mAh power bank (actual capacity: 13,300mAh), you can charge tablets and laptops about 1.5 times. For some exceptionally large laptops, like the MacBook Pro 16 inches, you need a 30,000mAh power bank.
Converting voltage: 25% capacity loss
Power banks only have 2/3 of the indicated capacity, mostly because the power has to be converted. The voltage of the battery in the power bank is 3.7 ampere, but the power bank has to raise the voltage to 5 ampere to charge a smartphone or a tablet. By increasing the voltage, only 7,4000mAh of 10,000mAh remains, for example, which is a quarter less. This applies to any power bank, regardless of the capacity or quality.
During charging: 10% energy loss
About 10 percent of the remaining energy is lost during charging. This reduces the 7400mAh from before to 7400 x 0.9 = 6660mAh. A lot of the energy dissipates as heat, which is why your smartphone often gets warm during charging. More expensive power banks from well-known brands are more efficient than cheap power banks. All our power banks have about 10% energy loss. With budget power banks, for example from Chinese wholesale websites, the loss can be as high as 30%. The extra heat that arises is also bad for your battery.