From the first time of mini-satellite to this time, Ni-Cd batteries has generally been used for power system of satellite because of its smooth discharge characteristics. It is now, in contrast to this, it has low energy density when compared with some other batteries. So, li-ion battery can be alternative to it in space applications. To achieve this goal, a circuit was designed to charge/discharge li-on battery, payload of our satellite (RASAT) which will be launched two years later, will be used as main energy sources for next satellite projects. Adding to this goal, circuit is designed to help Ni-Cd battery at some specific time of operation.