An external battery is a portable power source designed to charge electronic devices like smartphones, tablets, and laptops. These batteries store electrical energy and can be connected to devices via USB or other charging ports, providing a convenient way to recharge on the go without needing a wall outlet. External batteries come in various sizes and capacities, measured in milliampere-hours (mAh), which indicates how much charge they can hold. Some models also feature multiple ports, allowing users to charge several devices simultaneously. They are especially useful for travelers or anyone who frequently uses their devices away from home.