An alternator voltage may be controlled based on a proportional gain scheduling in response to an engine load of an internal combustion engine and/or a state of charge (SOC) deviation for a battery based on a target SOC of the battery and an actual SOC of the battery. The alternator voltage may be a voltage less than a current battery voltage under high engine loads to enable the battery to power an accessory system and the alternator voltage may be a voltage greater than a voltage of the battery under low engine loads or engine loads less than high engine loads to enable the alternator to charge the battery.