A USB Power Bank is a portable charger that allows you to charge your devices without the need for an electrical outlet. It works by storing energy in a rechargeable battery pack and then transferring this energy to your device when it needs it. The Levo PA71 is a great example of a USB Power Bank, as it has a 7,000 mAh capacity and can be used to charge up to three devices at once. It also has two USB ports for charging, making it ideal for people who need to charge multiple devices at once. With its slim design and lightweight construction, the Levo PA71 is easy to carry around and store in tight spaces.