**6.2 Types of batteries**

Lead acid, Lithium ion, Nickel metal hydride, Nickel cadmium, sodium sulphur, Sodium Nickel chloride, redox flow and zinc air batteries are mostly used in energy storage system. Each type of battery has their own characteristic like storage capacity, life time cycle, cost and charging/discharging cycles. Sodium sulphur batteries response very quickly and their life cycle is about 15 years, but are expensive [45]. For small amount of storage applications, Lithium ion and nickel cadmium are attractive, but for higher amount of energy storage applications these batteries are expensive. According to IRENA 2015b, storage technology is chosen on the base of their parameters [46].

#### **6.3 Lead acid batteries**

This type of battery has low cost, and deep cycle, and are used in industrial applications as well as in on grid application since hundred years. But, due to their lower specific energy and power, lower cycle life and longer charging time, their capacity in large capacity renewable energy is less as compare to sulphur and Lithium ion batteries. These batteries are well suited for frequency regulation applications because of their low upfront cost, and with the advancement in research it is aimed to increase life cycle, charge acceptance, cost reduction, discharge performance. To improve the power active materials having low internal resistance and life cycle is improved using enhancing the design [9].
