In a lead-acid storage battery, pbo2 is reduced to

Lead-Acid storage battery is a secondary cell which can be recharged by passing current through it in the opposite direction.

Following is the overall chemical reaction operative during discharging of lead-acid battery:

Pb (s) + PbO2 (s) + 2H2SO4 (aq) → 2PbSO4 (s) + 2H2O (l)

From above reaction, it can be seen that oxidation state of lead in PbO2 and PbSO4 is + 4 and + 2 respectively. Thus, upon discharging lead oxide is reduced to lead sulphate in lead-acid storage battery.