A power management system having automatic calibration is disclosed. The power management system may have an alternator and an electronic control unit. The electronic control unit may be configured to determine a reference voltage based on at least one measured operating condition of the alternator. The reference voltage may correspond to an overloading threshold of the alternator. The electronic control unit may be further configured to monitor a voltage of the alternator and, when the monitored voltage is less than the reference voltage, perform a corrective action to increase a power output of the alternator.