What is a secondary cell? Write the equation for the cathodic reaction of lead storage battery ?

Explanation

Cell which can be recharged by passing current through it in the opposite direction and used repeatedly are known as secondary cell.
Anode : `Pb(s) +SO_4^(2-)(aq) to PbSO_4(s) + 2e^(-)`
Cathode : `PbO_2(s) + SO_4^(2-) (aq) + 4H_4(aq) + 2e^(-) to PbSO_4 (s) + 2H_2O(l)`
Overall : `Pb(s) + PbO_2(s) + 2H_2SO_4 (aq) to 2PbSO_4(s) +2H_2O(l)`