A power bank, also called a portable charger, is a compact energy storage device built with lithium battery cells and an intelligent control board. It stores electricity in advance and delivers power to mobile phones, tablets, wireless earbuds, cameras and smartwatches when wall power is unavailable. Inside the unit, the BMS smart chip manages input and output current. It converts stored battery voltage into stable 5V, 9V or 12V output to match different electronics. Many modern models support PD and QC fast charging, which greatly cuts charging time for compatible devices. Power banks are popular for commuting, business travel, camping and outdoor work. They free users from fixed power sockets. Different sizes cover different needs: slim low-capacity ones for pocket carry, and high-capacity versions for long trips. Thanks to lightweight designs and wide compatibility, power banks have become essential accessories for digital users worldwide. They offer simple, reliable backup power anytime and anywhere.