A power system includes a primary bus connected to a traction battery, a secondary bus connected to an auxiliary battery, a power converter between the traction and auxiliary batteries, and a controller. The controller commands the power converter to increase a magnitude of current output to the secondary bus when an amount of charge current received by the traction battery exceeds a first amount threshold and commands the power converter to decrease the magnitude when an amount of charge current received by the auxiliary battery exceeds a second amount threshold.