State of charge modeling of lithium-ion batteries using dual exponential functions

A mathematical model is developed by fitting the discharging curve of LiFePO4 batteries and used to investigate the relationship between the state of charge and the closed-circuit voltage. The proposed mathematical model consists of dual exponential terms and a constant term which can fit the characteristics of dual equivalent RC circuits closely, representing a LiFePO4 battery. One exponential term presents the stable discharging behavior and the other one presents the unstable discharging behavior and the constant term presents the cut-off voltage. •The math model based on characteristics of equivalent circuits of batteries is built.•The developed model well describes the discharging behaviors of LiFePO4 batteries.•The impact of storage time and cycle number on discharging behaviors is predicted.•The accuracy of this model is very high; most RMSE is between 0.002 and 0.5.•The proposed model can be used to distinguish batteries under various conditions.