This graduate thesis describes the simulation and the design of the synchronous buck converter used for charging and discharging LiFePO4 batteries. The complete system is designed to charge or discharge any Li-ion battery with controllable load current. Active and passive components as well as the coolers were selected appropriately, as was the range of acceptable input resistive loads for battery drainage. The converter-battery system was mathematically modeled in state space, after which the model was averaged. From the averaged model, a transfer function was calculated regarding to the battery current. Using pole placement method the regulator parameters were obtained, followed by a z-transformation of the regulator itself. Simultaneously with the simulation, the electronic subsystem for signal amplification, optical separation and signal measurement was also designed. Appropriate electrical schematic was created, according to which the printed circuit board was designed. The PCB was routed and manufactured. Next, the electronic components were installed and soldered to the board. A system control firmware was written for the embedded microcontroller, which was firstly loaded with the bootloader, and secondly with the battery charger/discharger controller firmware. The system was successfully tested to the current reference change. The rise and fall times were satisfactory for usage or further testing.