A method for charging an energy storage system (ESS) from an AC line voltage having differing input voltages (e.g., 120 Vac or 240 Vac), the method includes a) determining which of the AC line voltages is provided for charging the ESS as a charging AC voltage; b) boosting the charging AC voltage to an intermediate voltage responsive to the provided AC line voltage; c) scaling, responsive to the particular one of the AC line voltages, the intermediate voltage to a secondary voltage using a scaling factor; and d) converting the secondary voltage to a charging voltage applied to the ESS.