Abstarct: Abstract Since it is important to determine the state of charge and the temperature of the central core of the battery with the aim of performing better, maintaining life, preventing risks, and increasing efficiency and security in lithium-ion batteries, Therefore, the attention of researchers has been directed to the accurate estimation of these parameters in recent decades. In this regard, according to the dependence of the parameters of the electrical-thermal model of the battery on the state of charge and the temperature of the central core of the battery, a completely non-linear model is developed in this thesis. For this purpose, at different temperatures, the complete discharge of the electric charge of the battery is carried out under controlled conditions, and the parameters of the electric-thermal model of the battery are extracted as a function of the state of charge and the temperature of the central core of the battery.Finally, the Kalman filter is applied to this model in order to accurately estimate the state of charge and the temperature of the core of the battery, and it is compared with common methods in which the model of the system has constant parameters in all temperatures and states of charge. The simulation results illustrate that the method proposed in this thesis at different temperatures and in the presence of noise has a much better performance in terms of average and standard deviation of estimation than the previous methods.