A battery locomotive is a train that runs on electricity stored in big batteries. The big batteries are filled with electricity from a source like a power plant or from the sun. When the train is traveling, the electricity stored in the batteries powers the train. When it's not moving, the energy stored in the batteries can be used to power the lights and other things inside the train. Battery locomotives don't need tracks or electricity lines, which makes them very useful for trains that must travel on special tracks or in places where there isn't a lot of electricity.