Regenerative braking
Slowing down with the motor working as a generator, which returns part of the car's energy of motion or height to the battery.
Explained in
Why does braking charge the battery?When the car slows down, the motor works as a generator. How much energy that returns depends on speed and height, and a little physics shows why.Regeneration therefore matters most where a car slows down often or descends: in town traffic and in the hills. On a flat motorway at constant speed, there is little to recover.