A method of operating a battery system comprising a plurality of battery cells (24, 26, 28, 30) coupled in series and a plurality of converter stages (14, 16, 18, 20), wherein each stage of the plurality of converter stages comprises an inductor (34, 40, 46, 52), a switch (S14, S24, S34, S44), and a capacitor (36, 42, 48, 54), and wherein the plurality of battery cells includes at least three battery cells coupled in series and each cell of the plurality of battery cells is associated with a converter stage of the plurality of converter stages, the number of battery cells being equal to the number of converter stages, the method comprising: determining a cell with a greatest charge excess of the plurality of battery cells; determining a cell with a greatest charge deficit of the plurality of battery cells; discharging the cell with the greatest charge excess in order to charge, with a voltage converter, the cell with the greatest charge deficit, wherein the discharging comprises: using a converter stage associated with the cell with the greatest charge excess as a source stage of the voltage converter, and using a converter stage associated with the cell with the greatest charge deficit as a sink stage of the voltage converter; wherein using a converter stage associated with the cell with the greatest charge excess as a source stage of the voltage converter, and using a converter stage associated with the cell with the greatest charge deficit as a sink stage of the voltage converter, comprises configuring the voltage converter as a single-ended primary inductor converter, SEPIC. the method comprising: determining a cell with a greatest charge excess of the plurality of battery cells; determining a cell with a greatest charge deficit of the plurality of battery cells; discharging the cell with the greatest charge excess in order to charge, with a voltage converter, the cell with the greatest charge deficit, wherein the discharging comprises: using a converter stage associated with the cell with the greatest charge excess as a source stage of the voltage converter, and using a converter stage associated with the cell with the greatest charge deficit as a sink stage of the voltage converter; determining a cell with a greatest charge excess of the plurality of battery cells; determining a cell with a greatest charge deficit of the plurality of battery cells; discharging the cell with the greatest charge excess in order to charge, with a voltage converter, the cell with the greatest charge deficit, wherein the discharging comprises: using a converter stage associated with the cell with the greatest charge excess as a source stage of the voltage converter, and using a converter stage associated with the cell with the greatest charge deficit as a sink stage of the voltage converter; using a converter stage associated with the cell with the greatest charge excess as a source stage of the voltage converter, and using a converter stage associated with the cell with the greatest charge deficit as a sink stage of the voltage converter; wherein using a converter stage associated with the cell with the greatest charge excess as a source stage of the voltage converter, and using a converter stage associated with the cell with the greatest charge deficit as a sink stage of the voltage converter, comprises configuring the voltage converter as a single-ended primary inductor converter, SEPIC.