Aiming at the problem that the Thevenin equivalent circuit model is not accurate enough to identify the parameters of lithium batteries a second-order RC equivalent circuit model was proposed to identify the parameters of lithium batteries. Methods The relevant data of lithium battery were obtained through a pulse discharge experiment and the least squares algorithm was used on MATLAB to identify the parameters of the established second-order RC equivalent circuit the changes of each parameter of the lithium battery under different states of charge were analyzed the accuracy of parameter identification was judged by calculating the terminal voltage of the lithium battery and the identification results were analyzed and compared with the results identified by the Thevenin equivalent circuit model. Results As the state of charge SOC of the lithium battery decreased the parameters of lithium battery fluctuated slightly. When the SOC of a lithium battery was at a low level the parameters of the lithium battery changed more drastically which was caused by the chemical concentration polarization of the lithium battery. When the identified parameters were used to solve the terminal voltage of the lithium battery it was found that the error fluctuation of the terminal voltages of the lithium battery was relatively stable over time and the maximum error did not exceed 0. 05 V. In contrast the error fluctuation of the terminal voltages obtained by using the Thevenin equivalent circuit model was large and the maximum error was more than 0. 08 V. Conclusion In the identification of lithium battery parameters the second-order RC equivalent circuit is more accurate than the Thevenin equivalent circuit which can better describe the dynamic and static characteristics of lithium batteries providing a strong basis for the subsequent estimation of the state of charge of lithium batteries.