A method comprising determining a respective impedance curve for a plurality of cells extracted from a plurality of rechargeable batteries, wherein each impedance curve is descriptive of an internal impedance of the respective cell as a function of frequency over a predefined frequency range; determining, for each of the plurality of cells, respective one or more impedance characteristics based on the impedance curve determined for the respective cell; and sorting the plurality of cells into one of a first quality class or a second quality class in accordance with the one or more impedance characteristics determined for the plurality of cells, characterized in that each impedance curve is derived via the following procedure: setting an impedance of an adjustable load (121, 131, 131', 141) coupled between terminals of the respective cell between two or more predefined values according to a multi-frequency pseudo-random pulse sequence, PRPS, that represents a plurality of frequency components at a predefined frequency resolution (f res) within the predefined frequency range and that defines switching between said two or more predefined values as a function of time, and deriving the internal impedance of the respective cell over the predefined frequency range based on a voltage across the terminals of the respective cell and an electric current supplied to the adjustable load (121, 131, 131', 141) as a function of time, and wherein said one or more impedance characteristics for a given cell comprise an indication of the number of partially circular segments appearing in a complex-plane representation of the impedance curve determined for the respective cell and respective frequency sub-ranges within which said partially circular segments appear. determining a respective impedance curve for a plurality of cells extracted from a plurality of rechargeable batteries, wherein each impedance curve is descriptive of an internal impedance of the respective cell as a function of frequency over a predefined frequency range; determining, for each of the plurality of cells, respective one or more impedance characteristics based on the impedance curve determined for the respective cell; and sorting the plurality of cells into one of a first quality class or a second quality class in accordance with the one or more impedance characteristics determined for the plurality of cells, characterized in that each impedance curve is derived via the following procedure: setting an impedance of an adjustable load (121, 131, 131', 141) coupled between terminals of the respective cell between two or more predefined values according to a multi-frequency pseudo-random pulse sequence, PRPS, that represents a plurality of frequency components at a predefined frequency resolution (f res) within the predefined frequency range and that defines switching between said two or more predefined values as a function of time, and deriving the internal impedance of the respective cell over the predefined frequency range based on a voltage across the terminals of the respective cell and an electric current supplied to the adjustable load (121, 131, 131', 141) as a function of time, and setting an impedance of an adjustable load (121, 131, 131', 141) coupled between terminals of the respective cell between two or more predefined values according to a multi-frequency pseudo-random pulse sequence, PRPS, that represents a plurality of frequency components at a predefined frequency resolution (f res) within the predefined frequency range and that defines switching between said two or more predefined values as a function of time, and deriving the internal impedance of the respective cell over the predefined frequency range based on a voltage across the terminals of the respective cell and an electric current supplied to the adjustable load (121, 131, 131', 141) as a function of time, and wherein said one or more impedance characteristics for a given cell comprise an indication of the number of partially circular segments appearing in a complex-plane representation of the impedance curve determined for the respective cell and respective frequency sub-ranges within which said partially circular segments appear.