The present invention provides a battery charger and battery charging method controlled with a charging waveform input of an AC-DC switching circuit to a DC link and a DC-DC stage converter for outputting a regulated DC voltage. The method determining the charging waveform comprising the steps of selecting a Pulse Width Modulation (PWM) zero-off charging waveform signal input to the AC-DC switching circuit and calculating a ripple power at the DC link based on the signal input power and output power of the regulated DC voltage output.