Many battery simulation models, but also electrochemical interpretations are based on impedance spectroscopy. However, the impedance of a battery is influenced by various factors, e.g. in the case of a lead–acid battery: state of charge (SOC), charging or discharging, superimposed dc current, short-term history or homogeneity of the electrolyte. This paper analyses the impact of those factors on impedance spectra of lead–acid batteries. The results show that very detailed information about the conditions during the measurement is crucial for the correct interpretation of a spectrum.