Both the engine / generator and the use of regenerative braking recharge the battery pack. (ucsusa.org)
The customer can also recharge the battery in the middle of the night, when prices are lowest in some markets, and then use the electricity during the day to reduce energy costs. (nissannews.com)
In addition, applying the brakes early for a slow, gradual stop doesn't increase brake wear, and it helps recharge the batteries for powering the electric motor. (cars.com)