Hybridization of cars can be mild and full and even depends on different drivetrains (components between the engine and driving wheels, also clutch and axle, and components of the driveline).
Features of Hybrid cars are:
Idle-Off: This feature makes the vehicle to shut down its gasoline engine when vehicle is stopped, which saves fuel. In a well-planned system, the engine will turn on and be able to go in very less time (less than time taken to move foot from the brake to the gas pedal).
Regenerative Braking: In a conventional car, mechanical brakes are used (friction) to stop. It transforms the kinetic energy into hot brakes and thereby wasting the energy. Regenerative braking maintains some of the stopping tasks which are done by friction brakes and uses the electric motor to stop the car.
Power Assist and Engine Downsizing: A vehicle has a big motor and battery pack, so that motor can improve the engine to accelerate the vehicle during driving. The power assist ability decreases the requirements of the gasoline engine, and helps in utilizing a smaller, more effective gasoline engine at the same time providing the same performance as that of a larger engine. Engine downsizing can be obtained by using physically smaller engines consisting of less cylinders or limited displacements, or can be gained by using more effective combustion cycles.
Electric-only-drive: This feature makes the car to drive by utilizing only the electric motor and battery pack. This provides complete benefit of electric side of the dual system. At low speeds and at the time of start, the electric motor and battery energizes the car ,and at high speeds the engine maintains car.
Extended Battery-Electric Range: This feature makes the hybrid car to operate completely as a battery-electric vehicle for nearly 20-60 miles, thus enhancing their environmental functioning, provided they are using good sources of electricity.
Hybrid cars are very expensive because they need bigger motors and battery packs to guarantee good vehicle performance and enough all-electric range.