Technology
To improve the fuel economy and efficiency of the 2009 3 Series, BMW has fitted each model with Brake Energy Regeneration. In simple terms, the technology controls the electrical system to only charge the battery while the vehicle is braking, coasting or decelerating. This unique approach transfers full engine power to the driven wheels during acceleration (to improve fuel economy), and utilizes the kinetic energy that is typically lost during deceleration to charge the electrical system (to improve efficiency). According to BMW, Brake Energy Regeneration improves fuel efficiency by upwards of three percent. The system is continuously monitored by the vehicle's electronics. If necessary, it will continue to charge the battery during acceleration to prevent the electrical system from being completely drained.

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