HOW IS IT THAT UNLIKE AN ORDINARY BATTERY OF A CAR GETS RECHARGED?

There are two kinds of batteries-primary and secondary.The chemical reaction responsible for the generation of electric current in a battery is not reversible in a primary battery.Hence,they cannot be recharged.They are often called dry cells,as the electrolytes (the chemical substance that conducts the electric current in a battery) used are generally paste or jelly-like and are convenient for use in torches and many home applicances.The secondary batteries have a liquid electrolute and their chemical reaction can be reversed.For example, in a lead-acid battery,lead and lead oxide react with sulphuric acid to produce lead sulphate and water.When all the sulphuric acid is consumed,(it may not be fully consumed but it does get diluted by the water produced), the battery loses its ability to produce electricity.It can then be recharged by forcing electrons,by means of a battery charger, to move in a direction opposite to that of the discharge.As a result,the chemical reaction is reversed and the electrode materials are restored,thereby increasing the sulphuric acid concentration.Such batteries are normally used in cars and other vehicles.