Rechargeable battery assembly (100; 200; 300; 400; 500; 600), comprising: a first rechargeable battery unit having a first terminal and a second terminal; a second rechargeable battery unit having a first terminal and a second terminal, said second rechargeable battery unit being connected in series with the first rechargeable battery unit ; and a differential amplifier having an inverting input, a non-inverting input and an output, at which an amplified difference between the signal at the inverting input and the signal at the non-inverting input is present; wherein - the non-inverting input of the differential amplifier is connected to the second terminal of the first rechargeable battery unit and to the first terminal of the second rechargeable battery unit , - the inverting input of the differential amplifier is coupled to the first terminal of the first rechargeable battery unit and to the second terminal of the second rechargeable battery unit , and - the output of the differential amplifier is connected to the second terminal of the second rechargeable battery unit ; characterized in that a coupling element having two load terminals is connected between the output of the differential amplifier and the second terminal of the second rechargeable battery unit , which coupling element enables the second rechargeable battery unit to be charged via the coupling element , but permits at most slight discharging of the second rechargeable battery unit in the direction of the output of the differential amplifier , wherein the first pole of the first rechargeable battery unit and the second pole of a third series-connected rechargeable battery unit serve as a voltage supply or a reference for the differential amplifier . a first rechargeable battery unit having a first terminal and a second terminal; a second rechargeable battery unit having a first terminal and a second terminal, said second rechargeable battery unit being connected in series with the first rechargeable battery unit ; and a differential amplifier having an inverting input, a non-inverting input and an output, at which an amplified difference between the signal at the inverting input and the signal at the non-inverting input is present; wherein - the non-inverting input of the differential amplifier is connected to the second terminal of the first rechargeable battery unit and to the first terminal of the second rechargeable battery unit , - the inverting input of the differential amplifier is coupled to the first terminal of the first rechargeable battery unit and to the second terminal of the second rechargeable battery unit , and - the output of the differential amplifier is connected to the second terminal of the second rechargeable battery unit ; - the non-inverting input of the differential amplifier is connected to the second terminal of the first rechargeable battery unit and to the first terminal of the second rechargeable battery unit , - the inverting input of the differential amplifier is coupled to the first terminal of the first rechargeable battery unit and to the second terminal of the second rechargeable battery unit , and - the output of the differential amplifier is connected to the second terminal of the second rechargeable battery unit ; characterized in that a coupling element having two load terminals is connected between the output of the differential amplifier and the second terminal of the second rechargeable battery unit , which coupling element enables the second rechargeable battery unit to be charged via the coupling element , but permits at most slight discharging of the second rechargeable battery unit in the direction of the output of the differential amplifier , wherein the first pole of the first rechargeable battery unit and the second pole of a third series-connected rechargeable battery unit serve as a voltage supply or a reference for the differential amplifier . <EOS>