You can charge your power bank using a USB connection and using the "In" port.
The charge is then stored in the power bank until it is withdrawn when you use it to charge a device. The capacity of each power bank is different.
Power banks eliminate the need to carry a regular charger because power banks can store energy.
There is complex circuit technology inside power banks. High-quality power banks have safety features to prevent overcharging and short-circuiting, as well as quick charging and wireless technology.