The aim of impedance-based modeling is to develop an equivalent circuit for the electrical characteristics of an energy storage device. Equivalent circuit models contain simple models consisting of a variable voltage source, an internal resistance, inductance, multiple RC elements as well as fractional models, which are capable of modeling special impedance characteristics by using Warburg elements or constant-phase elements. Other models are designed especially for the high frequency behavior of a cell. The equivalent circuits and the values for the various elements can be determined through impedance spectroscopy or the evaluation of the voltage response to a current pulse (for further information about characterization see Electrical characterization). By fitting the impedance spectra and the voltage responses, the model parameters can be extracted.
For all battery types the impedance spectrum/voltage response is altered by a variety of external influencing factors, primarily DC ripple current, temperature and state of charge. As a result, a broad range of measurements are required for the various tasks performed by a battery. A further issue is the size of batteries and the associated irregularity in temperature, power distribution, etc.