The C-Max Energi has an EV mode button on the center stack that lets the driverchoose between three modes: electric-only driving, normal hybrid mode (which blends electric and gasoline engine power as appropriate) or EV-later mode, which reserves the battery pack power for later use.
Regardless of how you choose to track your auto expenses, the knowledge you get from doing so will put you in the driver's seat when it comes to figuring out how much your vehicle is costing you to operate and documenting its value when it's time to get rid of it.