Abstract <p>Based on the analysis of electrochemical processes occurring in nickel–iron batteries, an electrical circuit of battery replacement is substantiated. A method for determining the parameters of the electrical replacement circuit for batteries of various electrochemical systems is proposed. Using the example of a nickel–iron battery of the TNZhK-U2 type, the parameters of the electrical replacement circuit are determined: ohmic resistance, polarization resistance, and polarization capacitance. Based on the results of experimental studies, analytical dependences of the polarization resistance and capacitance on the discharge current and the degree of charge of the battery are obtained. It is shown that, with an increase in the discharge current and the degree of charge of the battery, their values decrease, and it has been found that, with an increase in the discharge current, the proportion of voltage drop on the ohmic resistance of the battery increases, which affects the voltage of the batteries when they are used as part of network electric energy storage devices and electric vehicles, since in such systems the resistance of metal jumpers and contacts is added to the ohmic resistance of the batteries.</p>