act: With the rapidly increasing use of portable equipment requiring high efficiency, simple chargers are essential. Advanced battery management systems need to provide adequate charging strategies for the battery pack in a fast, safe, and reliable manner. The aim of this thesis is to design an optimal controller for rechargeable lithium ion battery. In order to, model the behavior of the lithium ion battery charge and discharge is investigated. In this dissertation, the nonlinear equivalent circuit model combined with thermal models are used. In order to confirm the non-linear equivalent circuit model lithium ion battery, an electrochemical model has been adapted. After verifying the model, using it to charge the battery and the constraints such as limits for current, temperature and voltage optimization problem to determine the optimal current for charging the lithium ion battery, is defined. Ohmic losses and charge time is considered in the cost function. by reduce ohmic losses, reduced heat generation and battery damage from excessive heat. Ohmic dissipation factor for weighting lo compare to charging time i used. Charge optimization problem for one cell i solved and then to a lithium ion battery consist of multiple cells is extended the nonlinear model of the lithium ion battery for optimal problem solving nonlinear differential equations need to be. In this thesis, in order to create an alternative charger which does not depend on model, A fuzzy controller is proposed for lithium ion battery. In the fuzzy controller, temperature and charging modes as input is proposed. The maximum current is injected into the battery is changed with temperature. This allows selection of the input temperature, At any temperature the current corresponding to the temperature injection. state of charge instead of voltage that i the previous studies was used that Precision fuzzy controller increases. The state of charge reaches to 70% voltage changes is very low and about a few hundredths. Another advantage of using state of charge mode, use it to recharge the lithium ion battery is composed of several cells. In this case, the battery charge is based on cell that have minimum state of charge, is charged. State of charge is not directly measurable, And the Adaptive Extended Kalman Filter is used to estimate it. Due to practical considerations for implementation in this thesis, Injection current to the battery is limited to a specified and fixed level. Keywords: Charge Lithium ion batteries, Nonlinear model, Charge optimization problem, Fuzzy controller, Practical considerations