The Batteries in Most Automobiles Are Lead-Acid Storage Batteries

Six cells producing 2 volts each are connected in series for a total of 12 volts.

Oxidation occurs at the anode:

Pb(s) + SO42−(aq) 

PbSO4(s) + 2e−

Reduction occurs at the cathode:

PbO2(s) + 4 H+(aq) + SO42−(aq) + 2e−  PbSO4(s) + 2 H2O(l)