An electric bicycle is a conventional bicycle that has been fitted with an electric motor. Most often electric bicycles or "e-bikes" are powered by rechargeable batteries however some experimental electric bicycles run directly on or recharge their batteries via solar panels, fuel cells, gas generators or other alternative energy sources. Using an on-board generator may impact the legal jurisdictional definition of an electric bicycle. A few types of electric bicycles are able to re-capture a small amount of energy from braking and can re-charge the batteries while braking or traveling down hills (regenerative braking).