Solar energy is a renewable source of energy. Usage of this energy can reduce the carbon emissions on the environment. To store electric energy produced from solar panels, a battery is used named solar battery. The capacity of storing electricity depends on the active materials of the battery cells. Normally the capacity of a lead acid battery depends on active materials, size of the plates, gravity of the acid, construction of the grid of the plates. In this research, all other variables responsible for battery capacity (gravity of acid, size of the plates, construction of grid etc.) are constant and only one variable is active materials of the plates. 4 batteries containing different amounts of active material are used to identify the best combination which gives the highest value of active mass utilization coefficient.