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What are Primary and Secondary Cells ?

Primary cells are cells in which the chemical reaction which produces the power is not reversible. That is, the cell cannot be charged.  A common example is the dry cell.  Primary cells are cheaper and find application in radios, flash lights, torches, etc.    

Secondary cells are those cells in which the chemical reaction can be reversed by passing an electric current in the reverse direction.  The active material of the battery is reformed and the battery is recharged.