What is battery? Explain the primary and secondary battery with example? 

Batteries are electrochemical cells which converts chemical energy into electrical energy during discharging and charging.

•  Primary batteries: The batteries, which produce electrical energy at the expense of free energy of active materials and produce energy only as long as active materials are present, are called as primary batteries. These are nonrechargeable batteries and are to be discarded after the use. The cell reactions is said to be irreversible. Example: Dry cell. Zn-air battery.
• Secondary batteries: The rechargeable batteries that produce electrical energy at the expense of free energy of active materials are called secondary batteries. These active materials are capable of restoring at respective electrodes on recharge and prepare for discharge once again. The cell reactions is said to be reversible. Example: Lead acid battery, Ni-MH battery, Li ion battery