In many types of stand alone photovoltaic (PV) systems for continuous power supply batteries are required to even out irregularities in the solar irradiation. This chapter is discussed about the various types and working principle of batteries with life and economics. The energy produced during the day, which wasn't consumed by loads, is saved in batteries. Saved energy can be used at night or during the days with bad weather conditions. Fundamentals, physical construction, charging-discharging, effect of temperature, selection of batteries of PV applications, operation and maintenance, circuits, sizing are also discussed. The calculations for life time of the batteries are discussed with solved examples.