Hybrid cars utilize a double engine (electric and conventional): an electric engine is associated with a conventional engine (e.g. petrol or diesel). During vehicle operation, therefore, you can use only the electric engine, only the internal combustion engine or both engines. The vehicle can travel short distances (e.g. 5 km) in electrical mode only at low speed. The total number of km which can be covered is determined by the available fuel and does not depend from the battery. The battery is recharged: Recovering the energy during braking / downhill and accumulating it in the battery as electric energy. Through the energy generated by the conventional engine, when the level of battery charge falls below a certain threshold.