© 2018 IEEE.Battery management system (BMS) was implemented at Li-ion based battery system using passive charge balancing method. Commonly, passive balancing technique is widely used in BMS because system implementation simple and cost is low. The battery system was created with four different lithium-ion battery cells. As it is known the most used battery type is Li-ion type battery in vehicles, so this battery type was selected in the study. Two main microprocessors were used as master and slave for management system. STM32f103C8 microcontroller was used as master and PIC18f4520 microcontroller used as slave controller in the BMS. Four battery cells voltages, currents and temperatures were controlled with designed control system. The information received from the current and voltage sensors was collected from each cell using slave controller and sent smoothly to the master controller system. These experimental results indicated that the passive balancing method was implemented and battery cells charged successfully.