Discharge and Charging of Lead-Acid Battery:

Within a lead-acid battery, two categories of lead are acted upon electro-chemically through an electrolytic solution of diluted sulfuric acid (H₂SO₄). A positive plate consists of lead peroxide (PbO₂) and the negative plate is sponge lead (Pb), display in Figure.

Figure Chemical Actions during Discharge

Whenever a lead-acid battery is discharged, the electrolyte divides within H₂ and SO₄.   The H₂ will combine with some of the oxygen that is formed on the positive plate to generate water (H₂O), and thus decrease the amount of acid in the electrolyte.  The sulfate (SO₄) combines with the lead (Pb) of both plates, forming lead sulphate (PbSO₄), as display in Equation (4-1).

PbO₂ + Pb +  2H₂SO₄ → discharge 2PbSO₄ + 2H₂O                  (4-1)