To characterize electrical losses of fuel cells or batteries, impedance spectroscopy (IS) or current interruption (CI) can be used. Analysis and parameter determination of impedance data is widely used. The system under study is usually represented by an equivalent circuit from which the system parameters can be determined. However, the analysis of current‐interruption data is often carried out with too simple circuits, e.g., using pure exponential behavior, because analysis in the time domain (CI) is often much more awkward than analysis in the frequency domain (IS). A comparative study has been carried out on the analysis of a relatively ideal electrical circuit, containing a pure capacitor, and a more realistic circuit where the capacitor is replaced by a constant‐phase element. Equations describing the response in the frequency and time domain are presented. Emphasis is put upon the analysis of circuits containing a constant‐phase element because impedance measurements clearly indicate the presence of such an element in many types of experiments, and because there is only limited literature available describing the behavior in the time domain.