A portable power source is a device that provides energy to a device or system. The most common type of portable power source is a BATTERY, which is a device that stores electrical energy and can be recharged. Batteries are used in many everyday items such as cell phones, laptops, and even cars. They are also used in medical devices, military equipment, and other specialized applications. Batteries come in a variety of sizes and types, and can provide different levels of power depending on the application.