Recuperation is the function of braking to regain energy and thus increase the range. All modern electric cars can that by standard. The application is very simple:
When you go down from the accelerator, the car starts to brake automatically. Anyone who already has some practice in it, drives with rarly using the break pedal. For example, when rolling to the red traffic light.
While recuperating the electric motor is working as a generator and converts from kinetic energy in to electrical energy. With this function, the range in mountains is not much lower than in the plane.
By the way:
As long as the battery has >97%, you do not always have the full regen performance. That's due to the fact, that the battery is so full to charge that fast.
