Brake Energy Regeneration.
Until now, taking your foot off the accelerator meant letting energy go unused. With Brake Energy Regeneration, the kinetic energy that would otherwise go to waste is now converted into electricity and stored in the battery.
As soon as the driver takes his foot off the accelerator or brakes, the alternator is connected to the engine and converts the excess kinetic energy into electricity. When the battery is fully charged, the alternator is disconnected from the engine. This reduces the strain on the engine and lowers emissions. This simultaneously saves fuel and provides more energy for acceleration.