Interesting article on the SAE home page discussing the difference in electronics between the hybrid and plug-in versions of the C-Max.
"Turning a hybrid electric vehicle (HEV) into a plug-in hybrid (PHEV) is more than adding cells to a battery pack, reflashing the controller, and installing a charger. The 2013 Ford C-Max and C-Max Energi are examples of what it takes to develop conventional hybrid and plug-in versions of the same vehicle—that is, many specific parts, software, and validation."
http://www.sae.org/mags/aei/11705
"Turning a hybrid electric vehicle (HEV) into a plug-in hybrid (PHEV) is more than adding cells to a battery pack, reflashing the controller, and installing a charger. The 2013 Ford C-Max and C-Max Energi are examples of what it takes to develop conventional hybrid and plug-in versions of the same vehicle—that is, many specific parts, software, and validation."
http://www.sae.org/mags/aei/11705