Power Bank Battery charging calculator

Here is a online calculator for power banks so that you can find out what size you need for your portable equipment.

maH or Capacity of Supply battery:

Output Voltage usually 5V  maH or Capacity of input battery  

Calculation The labeled capacity on the power bank x 3.7 / output voltage of the power bank x 0.85 / the battery capacity of the of the drive = total number of charges for the device.

For example, the iPhone X has a battery size of 2,716mAh . With the formula, you would be able to expect up to 4.6 recharges from 20,000mah power bank. 

(20,000×3.7 / 5) x 0.85 / 2,716 mAh = 4.6 recharges

3.7 – The first multiple is the 3.7. There are different levels of voltage that a battery cell can have but the average voltage of a battery cell is 3.7v. Li-ion batteries that feature manganese also average at 3.7 volts. Li-ion batteries that feature cobalt average at about 3.6v.

0.85 – The first 3 digits in the brackets are multiplied by the 0.85. All power banks aren’t 100% efficient when giving power to devices, instead of giving 100% efficiency to the device, power banks lose some of their efficiency through heat due to energy transfers.