Lithium ion batteries are widely used in portable electronic devices and electric vehicles. Although battery technology has been significantly improved, it does not fully meet the energy requirements of electric vehicles. Electric vehicle batteries are built by serial and parallel connections of many cells to provide sufficient power. Differences between cells during battery usage can shorten the battery life and even worse can cause fire and explosion. Therefore, there is a need for a battery management system to ensure that the voltage, temperature and current information of the battery cells are used as optimum conditions. Cell balancing should be used to ensure that the battery cells are charging simultaneously. Cell voltage and temperature are measured by connecting auxiliary slave board to each series battery pack. This information is controlled by a master board. In this application, the excess energy is converted to heat by the load resistor on the utility boards. Fuzzy logic control is used to control the load resistor with the switching element. The charge status of the battery was estimated using the main battery current and the mains voltage with the master board. This application has been tested on an electric vehicle. A low cost modular battery management system has been developed that can control the safe charging and discharging of the vehicle battery.