Batteries A battery is a combination of cells either in series or parallel or both, in order to get the required amount of electrical energy. It is a portable source of electrical energy. The galvanic cells used to form batteries can be classified as: 1.Primary cells: In these cells, the chemical energy is converted into electrical energy as long as the chemical components are active. 2.Secondary cells: In these cells, the redox reaction that converts chemical energy into electrical energy can be reversed by passage of current.

Anode

Component s of a Battery

Cathode

Electrolyte

Separator

It contains active materials which spontaneously take part in the oxidation reactions. It contains active materials which spontaneously take part in the reduction reactions. It helps in the migration of the ions leading to the generation of electrical energy. It is a thin polymeric membrane which prevents the mixing of products formed at the electrodes.

Discharging and Charging of a Battery
The process in which spontaneous redox reaction occurs is called discharging. The process of conversion of an inactive material back into active materials in a cell is called charging.

Characteristics of a Battery
1.Voltage or EMF: •. It depends on the change in free energy of the reaction. •. According to Nernst equation,

•. A good battery is one which has a flat discharge rate (constant EMF)

1.Current: It is a measure of the rate of discharge reactions of the cell. It depends on the amount of active materials. Higher the amount of active materials, longer will be the time for which EMF is generated. 2.Current capacity: It is defined as the amount of current generated in unit time. It is measured in terms of ampere-hour (A h) and depends on the discharge conditions. 3.Power density:

4.Energy density:

1.Energy efficiency:

2.Cycle life: It is applicable