Originally Posted By: yugrus
I guess I can contribute to the subject as well. GM has some charging system in trucks like mine that is more advanced then many. It constantly monitors battery's SOC, and adjusts alternator output accordingly. So with my daily battery charging regime, the alternator produces 14.7 for about 4 minutes, up to the point that computer realizes that the battery is fully charged. Then the voltage drops to 12.6v, and could stay there for 30 minutes of driving, maybe more. Then it goes up to between 13.7-14.7. Then, after a while it drops back to 12.6V.
That is when the ambient temp is above 5C or so. When it is cold though, the voltage would never drop below 13.7V, and goes as high as 15V, so the software doesn't care about SOC, maybe it is trying to keep the battery warm? In any case, GM charging system would totally give you credit for the fully charged battery under normal conditions, and it will get it back to full charge quite fast after the start-up.
I think you'll find this is done to get the most MPG: charging voltage goes up when braking or coasting, or if the SOC drops low, and drops when accelerating