Abstract: A method for determining an ageing parameter KSOH of a rechargeable battery, especially a lithium rechargeable battery, featuring the steps (a) detecting an impedance Z of the rechargeable battery at different frequencies f, so that a Nyquist plot and a real part path, which plots a real part of the impedance Z against the frequency f, are obtained, determining at least one of the following SOH parameters, which can be selected from a predetermined list, establishing an SOH row vector {right arrow over (PSOH)} from the SOH parameters and all mixed terms of the form pSOH,m·pSOH,n, m=1, . . . , 11, n=1, . . . , m. The invention provides for the multiplication of the SOH row vector {right arrow over (PSOH)} by a saved calibration vector {right arrow over (ASOH)}, thereby obtaining the ageing parameter KSOH.