A direct current (DC) power source includes a rechargeable battery and a battery charging circuit, and supplies an output voltage within a specified output voltage range to at least one output port. In one embodiment, the power source determines whether an input voltage is present at an input port, where the input voltage is usable to produce a battery charging voltage during normal operation of the charging circuit. The power source also determines whether at least one load device is coupled to the output port(s). When the input voltage is present at the input port and at least one load device is coupled to the output port(s), the power source electronically decouples the rechargeable battery from the charging circuit, electronically adjusts a voltage at an output of the charging circuit so as to be within the specified output voltage range, and provides the adjusted voltage to the output port(s).