I have noticed that the 12v battery normally tests at 12.2 v or approx. 65% when driving daily. I assume that this is by design. I know that it just serves low amperage loads and is not needed for cranking a high draw starter motor. I wonder if it is better for its life expectancy or for some other reason to maintain it at a reduced state of charge. I have always tried to keep all my automotive batteries in a state of full charge, but everything about this car is different, so... Why would they engineer this charging circuit to maintain the 12v battery at less than a full state of charge? Inquiring minds need to know.