Abstarct: The increasing need for store electrical energy due to various reasons, such as distributed generation, grid backup energy, grid frequency regulation, etc., developed different types of battery chargers for saving energy. Most of these chargers receive their needs of energy from grid, which increasing the number of them causes adverse harmonic effect on the power grid and brings power quality issues. Hence, PFC converters are one of the most important requirements for modern industrial power systems. Another important issue on the charger is the amount time spent to recharge the battery that specially find relevant for batteries with cyclic application. This thesis aims to design PFC charger baxse on three-switch Buck converter. The reasons of choosing this converter are simple controllability and its cost-effectiveness due to the fewer numbers of switches is used. This charger is controlled with PI compensator and it has good responses in disturbances condition such as suddenly changes in three phase input voltage. This system is used for charging lead-acid battery, by applying desire charging algorithm. The explained procedure is simulated in SIMUlixnk environment of MATLAB. The simulation result shown that by development of multistep constant current charging algorithm to multistep constant current – constant voltage (the proposed algorithm), the battery charging time has reduced significantly.