BMW has released more details on the 7-Series Activehybrid that will be debuting in Paris next month. We now know a few elements that differ from the Mercedes-Benz S400 BlueHybrid. While the Mercedes has the lithium ion battery mounted in the engine compartment, the BMW has its battery in the trunk. The BMW also one-ups the Benz in the transmission department with an 8-speed automatic. The power electronics module is mounted under the floor of the trunk. BMW claims the ActiveHybrid 7 wil get a 15 percent reduction in fuel consumption and emissions compared to the standard 750i. The use of the hybrid motor as the alternator turns out to be more efficient than a conventional belt driven unit. The electrical power output during regenerative braking is ten times what can be achieved from a standard alternator without the parasitic losses. While the Mercedes uses only the 120V lithium ion battery to provide all electrical power to the vehicle, the BMW retains the same 12V Absorbent Glass Mat batteries used in other BMWs with brake energy regeneration. The 7-series hybrid uses the 120V electrical network in parallel with the 12V network to drive accessory systems ranging from the air conditioning to the adaptive damping. You can read all about it here.