A marine propulsion system includes an engine effectuating rotation of an output shaft, a battery, an alternator having a rotor driven into rotation by the output shaft and that is configured to generate a charge output to the battery, a battery state of charge sensor configured to measure a battery charge value of the battery, and a control system. This control system is configured to receive a demand value and/or a temperature, receive the battery charge value from the battery state of charge sensor; and control the alternator to adjust the charge output based on at least one of the battery charge value and the demand value and/or temperature.