An apparatus for charging and balancing a plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d), the apparatus comprising: first and second input terminals (1304, 1306) for providing a charging voltage to the plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d); a transformer including a primary side and a secondary side; a single high-side switch, a single low-side switch and a resonant tank circuit (1316, 1320), wherein the primary side is coupled to the single high-side switch and to the single low-side switch is further coupled to the resonant tank circuit (1316, 1320), and is associated with the charging voltage, the resonant tank circuit (1316, 1320) comprises a capacitor and an inductor coupled in series between the primary side and a node between the single high-side switch and the single low-side switch, the resonant tank circuit (1316, 1320), the single high-side switch and the single low-side switch are configured to operate in a resonant mode, and the secondary side includes a plurality of portions each coupled across a respective at least two of the plurality of series-connected battery cells; a plurality of first switches each coupled between a respective single portion of the secondary side and a corresponding first battery cell (1302a, 1302c) of the at least two of the plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d) and configured to provide a charging current to the first battery cell (1302a, 1302c) during a first half of a cycle of a current in the primary side of the transformer; and a plurality of second switches each coupled between the respective single portion of the secondary side and a corresponding second battery cell (1302b, 1302d) of the at least two of the plurality of series-connected battery cells and configured to provide a charging current to the second battery cell (1302b, 1302d) during a second half of the cycle of the current in the primary side of the transformer; and wherein each of the plurality of portions of the secondary side is configured to have a first polarity during the first half of the cycle of the current and a second polarity opposite the first polarity during the second half of the cycle of the current, and wherein energy is taken from the entire stack of the plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d) and redistributed back to the stack from the resonant tank circuit (1316, 1320) based on the battery cell that needs more energy than the other battery cells. first and second input terminals (1304, 1306) for providing a charging voltage to the plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d); a transformer including a primary side and a secondary side; a single high-side switch, a single low-side switch and a resonant tank circuit (1316, 1320), wherein the primary side is coupled to the single high-side switch and to the single low-side switch is further coupled to the resonant tank circuit (1316, 1320), and is associated with the charging voltage, the resonant tank circuit (1316, 1320) comprises a capacitor and an inductor coupled in series between the primary side and a node between the single high-side switch and the single low-side switch, the resonant tank circuit (1316, 1320), the single high-side switch and the single low-side switch are configured to operate in a resonant mode, and the secondary side includes a plurality of portions each coupled across a respective at least two of the plurality of series-connected battery cells; the primary side is coupled to the single high-side switch and to the single low-side switch is further coupled to the resonant tank circuit (1316, 1320), and is associated with the charging voltage, the resonant tank circuit (1316, 1320) comprises a capacitor and an inductor coupled in series between the primary side and a node between the single high-side switch and the single low-side switch, the resonant tank circuit (1316, 1320), the single high-side switch and the single low-side switch are configured to operate in a resonant mode, and the secondary side includes a plurality of portions each coupled across a respective at least two of the plurality of series-connected battery cells; a plurality of first switches each coupled between a respective single portion of the secondary side and a corresponding first battery cell (1302a, 1302c) of the at least two of the plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d) and configured to provide a charging current to the first battery cell (1302a, 1302c) during a first half of a cycle of a current in the primary side of the transformer; and a plurality of second switches each coupled between the respective single portion of the secondary side and a corresponding second battery cell (1302b, 1302d) of the at least two of the plurality of series-connected battery cells and configured to provide a charging current to the second battery cell (1302b, 1302d) during a second half of the cycle of the current in the primary side of the transformer; and wherein each of the plurality of portions of the secondary side is configured to have a first polarity during the first half of the cycle of the current and a second polarity opposite the first polarity during the second half of the cycle of the current, and wherein energy is taken from the entire stack of the plurality of series-connected battery cells (1302a, 1302b, 1302c, 1302d) and redistributed back to the stack from the resonant tank circuit (1316, 1320) based on the battery cell that needs more energy than the other battery cells.