An energy transformer for a battery system is disclosed. The energy transformer includes a plurality of DC/DC converters each having a first and a second input and a first and a second output. The first output of a first of the DC/DC converters is connected to a first output of the energy transformer and the second output of a last of the DC/DC converters is connected to a second output of the energy transformer. The first and second inputs are designed for connecting a battery module. The DC/DC converters are connected in series on the output side. The energy transformer has a plurality of first diodes each of which have an anode connected to the first input of one of the DC/DC converters and a cathode connected to the second input of another DC/DC converter so that the DC/DC converters are connected in series on the input side and via a second diode having an anode connected to the first input of the first of the DC/DC converters and a cathode connected to the first output of the energy transformer.