Ford C-MAX Energi is a five-passenger multi-activity vehicle offering high mileage and low emissions as well as distinctive body design and a flexible interior. The plug-in hybrid provides maximum fuel efficiency by pairing a high-voltage lithium-ion battery and electric traction motor with a high-efficiency Atkinson-cycle gasoline engine. This means the gasoline engine does not have to run all the time.
Best part!!!

The advanced lithium-ion battery system developed and assembled in-house by Ford in Michigan!!!!!!!!!

As I talked about in my book Build Your Own Plug-in Hybrid Electric Vehicle from my Green Guru Guides series and as Ford agrees:
 
C-MAX Energi photo
C-MAX Energi photo
In general, plug-in hybrid electric vehicles (PHEV) offer several benefits, including:
• Potential consumer savings on energy/fuel costs thanks to improved fuel efficiency over a standard hybrid
• Reduced dependency on petroleum and increased energy independence
Ford C-MAX Energi
Ford C-MAX Energi
• Reduced environmental impact through reductions in greenhouse gas emissions
• Increased use of electricity from renewable energy sources (e.g. wind and solar), where available, for vehicle recharging 

C-MAX Energi owners will have access to a suite of driver information systems – on-board and off-board – designed to help them manage the recharge process, plan the most eco-friendly route, monitor battery state of charge and maximize energy efficiency to extend use of electric mode.  

• MyFord Touch™ driver connect technology offers unrivaled configurability of vehicle information, including fuel level, battery power level, average and instant miles per gallon

• MyView option allows access to electrical demand data, which influences fuel economy and pure electric driving range
• Brake Coach helps coach drivers to optimize their use of the vehicle’s regenerative brakes to recapture kinetic energy and send it back to the battery, also reducing wear on the brakes
• C-MAX Energi offers MyFord Mobile, which is a smartphone app and website for monitoring key vehicle functions and charge settings while mobile

Source: Ford Motor Company