A battery charger comprising: first and second DC-link conductors (30a, 30b); an AC-to-DC rectifier connected to the first and second DC-link conductors and configured to convert AC voltages into a DC-link voltage across the first and second DC-link conductors; and a DC-to-DC converter comprising first and second pairs of output terminals (76, 78, 88, 90), first and second input terminals (32, 34) connected to the first and second DC-link conductors, a first switch connected to one of the first pair of output terminals, a second switch connected to one of the second pair of output terminals, and a multiplicity of power switches connected in series across the first and second input terminals, wherein the DC-to-DC converter is configured to output DC current for charging a low-voltage battery connected to the first pair of output terminals as a function of the DC-link voltage when the first switch is closed and the second switch is open and is further configured to output DC current for charging a high-voltage battery connected to the second pair of output terminals as a function of the DC-link voltage when the first switch is open and the second switch is closed, wherein the DC-to-DC converter is further configured to operate in a resonant converter mode when the first switch is closed and the second switch is open and to operate in a buck converter mode when the first switch is open and the second switch is closed, characterized in that the multiplicity of power switches comprise first, second, third and fourth power switches (60a-60d), another of the second pair of output terminals is connected to the second input terminal, and the DC-to-DC converter further comprises: an inductor connected to a midpoint between the second and third power switches; a transformer comprising a primary winding and a first secondary winding, a first terminal of the primary winding being coupled to the midpoint between the second and third power switches by way of the inductor, the primary winding connecting the inductor to the second switch; and a first capacitor coupling a second terminal of the primary winding to the second input terminal. first and second DC-link conductors (30a, 30b); an AC-to-DC rectifier connected to the first and second DC-link conductors and configured to convert AC voltages into a DC-link voltage across the first and second DC-link conductors; and a DC-to-DC converter comprising first and second pairs of output terminals (76, 78, 88, 90), first and second input terminals (32, 34) connected to the first and second DC-link conductors, a first switch connected to one of the first pair of output terminals, a second switch connected to one of the second pair of output terminals, and a multiplicity of power switches connected in series across the first and second input terminals, an inductor connected to a midpoint between the second and third power switches; a transformer comprising a primary winding and a first secondary winding, a first terminal of the primary winding being coupled to the midpoint between the second and third power switches by way of the inductor, the primary winding connecting the inductor to the second switch; and a first capacitor coupling a second terminal of the primary winding to the second input terminal.