A power bank is a portable battery that can be used to charge electronic devices such as smartphones, tablets, and laptops while on the go. Power banks come in various sizes, with the smallest ones being credit card-sized and can fit in a wallet or purse, while the biggest ones can be the size of a small carry-on luggage with a handle.

Power banks can be used to charge devices that have a USB charging cable. They can also support wireless charging, allowing users to simply place their device on the power bank to charge. Some power banks even come with solar panels that allow them to be charged over time, for example when left on a window sill for a few days.

Power banks can have different capacities, which are measured in milliampere-hours (mAh). The larger the capacity, the more power the power bank can store and the more times it can charge your devices. Power banks with USB-C should be considered for quickly charging the power bank itself, as well as using USB-C from the power bank to charge your devices.

When choosing a power bank, it's important to consider the power output, as well as the number and types of ports it has. Power banks may also come with features like LED lights, which can be useful in emergencies or when camping. Some power banks are also designed to be waterproof, shockproof, or dustproof, making them suitable for outdoor activities.

The main power bank brands include Anker, RavPower, Belkin, and Mophie, among others. Overall, power banks are a convenient way to keep your devices charged while on the go, providing an alternative to traditional wall outlets and USB charging ports.