I think it would be useful to know what everyone's 12 volt battery voltage is after the car has not been run for awhile, such as first thing in the morning or several hours after using it. I am seeing 12.4, which is below the optimum of 12.6, but perhaps it's somewhat normal for the C-Max? Let's find out! General instructions (open to refining) 1. Measure before driving the car, or several hours after driving it to eliminate the charging impact. 2. Measure from one of the 12-volt outlets, or the jumping connections under the hood. 3. If measuring inside the car, allow the various circuits and light that are activated by opening the door to go off before recording the voltage. 4. If measuring under the hood, leave it unlatched the night before to get access without triggering the interior circuits.