A computer-implemented method of estimating a battery state of an electrochemical battery, the method comprising: providing a series of electrical impedance measurements of an electrochemical battery, each electrical impedance measurement being measured at a respective measurement frequency (f s), the series being ordered according to the respective measurement frequencies, optionally, translating and/or scaling, in the complex plane of the electrical impedance, the series of electrical impedance measurements, characterized in that the method further comprises: weighting the electrical impedance measurements according to a weighting function that is dependent on the index (s) of the series or on the measurement frequency (f s), resulting in at least a series of consecutive elements of the series of measurements, when point-to-point connected in the complex plane of the electrical impedance in a sequence according to the index (s) of the series of measurements, forming at least one loop in the complex plane, wherein the weighting function increases with increasing measurement frequencies (f s), calculating a measure of the size of the at least one loop in the complex plane, wherein calculating the measure of the size of the at least one loop includes calculating one of: an area in the complex plane enclosed by the at least one loop; an extension of the at least one loop, or a length in a direction of maximum extension of the at least one loop, determining an estimation of a battery state of the electrochemical battery based on the calculated measure of the size of the at least one loop in the complex plane, and outputting the estimation of the battery state. providing a series of electrical impedance measurements of an electrochemical battery, each electrical impedance measurement being measured at a respective measurement frequency (f s), the series being ordered according to the respective measurement frequencies, optionally, translating and/or scaling, in the complex plane of the electrical impedance, the series of electrical impedance measurements, characterized in that the method further comprises: weighting the electrical impedance measurements according to a weighting function that is dependent on the index (s) of the series or on the measurement frequency (f s), resulting in at least a series of consecutive elements of the series of measurements, when point-to-point connected in the complex plane of the electrical impedance in a sequence according to the index (s) of the series of measurements, forming at least one loop in the complex plane, wherein the weighting function increases with increasing measurement frequencies (f s), calculating a measure of the size of the at least one loop in the complex plane, wherein calculating the measure of the size of the at least one loop includes calculating one of: an area in the complex plane enclosed by the at least one loop; an extension of the at least one loop, or a length in a direction of maximum extension of the at least one loop, determining an estimation of a battery state of the electrochemical battery based on the calculated measure of the size of the at least one loop in the complex plane, and outputting the estimation of the battery state. weighting the electrical impedance measurements according to a weighting function that is dependent on the index (s) of the series or on the measurement frequency (f s), resulting in at least a series of consecutive elements of the series of measurements, when point-to-point connected in the complex plane of the electrical impedance in a sequence according to the index (s) of the series of measurements, forming at least one loop in the complex plane, wherein the weighting function increases with increasing measurement frequencies (f s), calculating a measure of the size of the at least one loop in the complex plane, wherein calculating the measure of the size of the at least one loop includes calculating one of: an area in the complex plane enclosed by the at least one loop; an extension of the at least one loop, or a length in a direction of maximum extension of the at least one loop, determining an estimation of a battery state of the electrochemical battery based on the calculated measure of the size of the at least one loop in the complex plane, and outputting the estimation of the battery state.