Based on the driving conditions, hybrid vehicles with automatic charging switch smoothly from the power supplied only by the internal combustion engine to the electric one to the combined one.
At low speeds and in stop-and-go traffic, the battery provides pure electric power for short distances, as well as more torque. During normal driving, it supplements the engine to save fuel. Regenerative braking recharges the battery to extend electric range.
When more power is needed or if the battery charge is low, the petrol engine takes over.