So, I'm researching getting a Ford C-Max Energi. It fits well with my commute range (approximately 20 miles a day). I understand that after the battery is depleted, a conventional motor kicks on and drive me the rest of the way. Based on my commute times, The conventional motor will only kick on for about 5-10% of my daily driving. Somehow I doubt this means that I will be able to get away with extending my regular oil change interval by 10-20 times it's regular length, as a 30,000 mile oil change interval seems unrealistic in the best circumstances.
So, can someone who knows how this is calculated explain it?