A power bank is a portable device that stores electrical energy and can be used to charge electronic devices, such as smartphones and laptops, when a power outlet is not available. Power banks typically use lithium-ion batteries to store the electrical energy, and they have a USB port or other type of charging port that can be used to charge electronic devices.

Power banks come in a range of sizes and capacities, and they can be recharged by plugging them into a wall outlet or other power source using the supplied charging cable. Some power banks also have additional features, such as the ability to charge multiple devices at the same time or to jump-start a car.

Power banks are useful for people who need to charge their devices when they are away from home or do not have access to a power outlet, such as when traveling or when camping. They can also be useful in emergency situations when the power is out and a device needs to be charged.