What driving task requires the most electricity?

I believe the answer is Starting the car.

When we start a car, we took up more than 0.5% of the existing power right from the side, and while driving it only took half of them.

Other elecricty generated task such as car lightning does not considered to take much power compared to this.

The driving task that requires the most electricity would be starting the car. The battery supplies the power to the car but the starter is what actually gets the engine started. The batter supplies power to the starter that in turn starts the motor.