Rechargeable fan can be used both indoor and outdoor, it has built in batteries. They have a USB port for charging and can be powered by a built-in rechargeable battery. You can adjust the speed of some of them to meet your cooling needs and they can be powered directly by batteries.Rechargeable fan can be used both indoor and outdoor, it has built in batteries. They have a USB port for charging and can be powered by a built-in rechargeable battery. You can adjust the speed of some of them to meet your cooling needs and they can be powered directly by batteries.