A power management system adjusts a first output voltage delivered to a load and adjusts a second output voltage delivered to a battery. The power management system includes an error amplifier for comparing the first output voltage with a first voltage reference indicative of an operating voltage of the load and for accordingly generating a first error signal. The power management system further includes a DC/DC converter for adjusting the first output voltage and the second output voltage by adjusting a duty cycle of the DC/DC converter and an error generator for controlling the duty cycle based on the first error signal. If the first output voltage is lower than the first voltage reference, the error generator reduces the duty cycle and a charging current of the battery based on the first error signal.