I have a 1991 150 hp model ELEIS (60 degree) all original. I have a question should the voltage gauge read 15 volts when running above 3500 rpm and then settled to 13.5 volts after you have run for a while above 3500 rpm? It never exceeds 15 volts and it seems the when the battery is fully charged the time it takes for the voltage to drop from 15 volts to 13.5 volts is less. Is this normal?