Battery charging with charge current throttling to assist minimum system voltage regulation

A battery charger is provided that includes a switching power converter that regulates an output voltage on an output voltage rail. A transistor couples between the output voltage rail and a rechargeable battery for a system. An error amplifier controls the conductance of the transistor based upon a difference between a battery current conducted by the transistor to the battery and a battery current threshold. A pulse width modulator controls a duty cycle of the switching power converter responsive to a selected error signal from a group of error signals. Based upon which error signal is selected for the duty cycle control, the battery charger either increases or decreases the battery current threshold to assist in keeping the output voltage above a minimum system voltage for the system.