A method of numerical representation for electrical storage cells based on measurement of wide frequency range impedance spectra at a number of different states of charge and measurement of the depth-of-discharge dependence of equilibrium voltage are developed. Applicability of this method to batteries with various chemistries and sizes are established by comparing numerical prediction to experiment. The model represents all tested batteries with accuracy (less than 1% in average deviation) in processes ranging from time constants of 1 ms to 10 h and from current densities of C/10 to 3C. The method includes the fitting of impedance spectra to physically relevant static linear transmission-line model and the use of parameters determined at different discharge levels to create a non-linear dynamic model. Formalization of the model as a non-linear equivalent circuit enables its direct application as a part of any electric device in digital circuit simulators like SPICE.