According to a first aspect of the invention a battery charger and method of charging a battery includes an input circuit that receive an ac input having a period of T seconds and provides a dc signal. A converter receives the first dc signal and provides a converter output across a dc bus having a peak voltage of V volts. An output circuit receives the dc signal and provides a battery charging signal having a power of P watts. A controller, controls the converter to provide power factor correction. A bus capacitor is connected across the dc bus and has a capacitance of at least (3PT)/(V.sup.2) farads, or a capacitance to store sufficient energy to maintain the available output power signal through the duration of mechanical transient. The capacitance may be at least (4PT)/(V.sup.2), (5PT)/(V.sup.2), or (5.5PT)/(V.sup.2). Multiple output circuits may be provided, connected either one at a time, or a number at a time.