A regulator voltage control includes measuring a current of a battery, determining a state of charge (SOC) of the battery based on the current, and determining a nominal optimum charging voltage as a function of the SOC of the battery. The nominal optimum charging voltage is converted to a % duty cycle, and a generator is operated relative to the % duty cycle for charging the battery. The nominal optimum charging voltage is reduced when either a battery charge current is below a predetermined value, or a current drawing accessory is turned on.