A system configured to charge with electric energy a first subset of storage cells and a second subset of storage cells from a storage comprising a serial arrangement of storage cells (101, 102, 103), the system comprising - a driver circuit configured to generate an AC voltage comprising a frequency component at an AC frequency from an electric energy source at a DC voltage; - a transformer comprising a primary inductor excited by the driver circuit and a first and a second secondary inductor (122, 322) which are magnetically coupled to the primary inductor; - a first resonance circuit configured to amplify and/or attenuate an amplitude of the AC voltage as a function of the AC frequency, to yield a first modified AC voltage; wherein the first resonance circuit comprises the first secondary inductor; wherein a gain of the first resonance circuit is at a maximum, if the AC frequency corresponds to a first resonance frequency of the first resonance circuit; and wherein the gain decreases from the maximum for AC frequencies which are higher or lower than the first resonance frequency; - a first rectifying unit configured to generate a first modified DC voltage from the first modified AC voltage, and configured to provide electric energy at the first modified DC voltage to the first subset of storage cells; - a second resonance circuit configured to amplify and/or attenuate an amplitude the AC voltage as a function of the AC frequency, to yield a second modified AC voltage; wherein the second resonance circuit comprises the second secondary inductor; wherein a gain of the second resonance circuit is at a maximum, if the AC frequency corresponds to a second resonance frequency of the second resonance circuit; and wherein the gain decreases from the maximum for AC frequencies which are higher or lower than the second resonance frequency; - a second rectifying unit configured to generate a second modified DC voltage from the second modified AC voltage, and configured to provide electric energy at the second modified DC voltage to the second subset of storage cells; and characterised in that the system comprises: - a controller which is configured to adjust the AC frequency in dependence on charging voltage requirements of the first subset of storage cells and/or the second subset of storage cells. - a driver circuit configured to generate an AC voltage comprising a frequency component at an AC frequency from an electric energy source at a DC voltage; - a transformer comprising a primary inductor excited by the driver circuit and a first and a second secondary inductor (122, 322) which are magnetically coupled to the primary inductor; - a first resonance circuit configured to amplify and/or attenuate an amplitude of the AC voltage as a function of the AC frequency, to yield a first modified AC voltage; wherein the first resonance circuit comprises the first secondary inductor; wherein a gain of the first resonance circuit is at a maximum, if the AC frequency corresponds to a first resonance frequency of the first resonance circuit; and wherein the gain decreases from the maximum for AC frequencies which are higher or lower than the first resonance frequency; - a first rectifying unit configured to generate a first modified DC voltage from the first modified AC voltage, and configured to provide electric energy at the first modified DC voltage to the first subset of storage cells; - a second resonance circuit configured to amplify and/or attenuate an amplitude the AC voltage as a function of the AC frequency, to yield a second modified AC voltage; wherein the second resonance circuit comprises the second secondary inductor; wherein a gain of the second resonance circuit is at a maximum, if the AC frequency corresponds to a second resonance frequency of the second resonance circuit; and wherein the gain decreases from the maximum for AC frequencies which are higher or lower than the second resonance frequency; - a second rectifying unit configured to generate a second modified DC voltage from the second modified AC voltage, and configured to provide electric energy at the second modified DC voltage to the second subset of storage cells; and - a controller which is configured to adjust the AC frequency in dependence on charging voltage requirements of the first subset of storage cells and/or the second subset of storage cells.