Charging control techniques for a vehicle including an engine that drives an alternator configured to charge a battery of the vehicle comprise modeling a fuel consumption of the alternator for each load level across a range of alternator loads using an engine torque model and a set of operating parameters of the engine, determining an energy output from the alternator for each load level across the range of alternator loads, calculating a cost-to-charge metric based on the modeled alternator fuel consumption and the determined alternator energy output for each duty cycle across a range of duty cycles of the alternator, determining an optimal cost-to-charge from the calculated cost-to-charge metrics, determining a target cost-to-charge metric based on a state of charge of the battery, and operating the alternator accordingly at an optimal duty cycle based on the metrics and current engine operating conditions.