Let's say you have a Power Bank with a capacity of 10.000 mAh and a phone with a battery capacity of 4.000 mAh. (Number of Device Charges) = (10.000 mAh × 0.85) / 4.000 mAh (Number of Device Charges) = 8.500 mAh / 4.000 mAh (Number of Device Charges) ≈ 2,13 In this example, the power bank can approximately charge the phone 2.13 times.
Battery capacity: The battery capacity is the amount of electrical charge that a power bank can store. It is usually measured in milliampere-hours (mAh). The higher the battery capacity, the more charge the power bank can store, allowing it to provide power for a more extended period.
That said, in practice, your 20,000mAh power bank won’t even provide a total smartphone battery charge of 14,800mAh, because there is one more factor that reduces its real total output. Reason 2: Inefficiency in the charging process also means that 20,000mAh of power bank charge equals noticeably less than 20,000mAh of smartphone battery charge.
If your 20,000mAh power bank can be assumed to have 14,800mAh of real, transferrable power, inefficiency will mean that it actually has 13,3200mAh of power it can transfer to your phone in total. As a result, a 20,000mAh power bank can actually charge a 5,000mAh smartphone around 2.66 times before needing a recharge itself.
So, a good 5,000 mAH wireless power bank such as Anker 621 MagGo will charge iPhone 15 with its 3200 mAH battery nearly one time fully in wireless mode and Samsung S24/S23, only about 80% as these have 4,000 mAH batteries. Here are some tips to maximize the power capacity of your power banks. PowerBank Guide is reader-supported.
For example, if your power bank has a capacity of 20,000mAh, multiplying this by 3.7 will reveal that it has total energy — as measured in mWh — of 74,000mWh. However, it will need to output at 5 volts to charge a smartphone, so dividing 74,000mWh by 5 — to convert back into mAh — will equal a smartphone battery charge of 14,800mAh.