Battery (All): Terminology: Discharge
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The process where a battery is under load and gives off current. During discharge, the lead on the negative plate and the lead oxide on the positive plate are converted to lead sulfate. Sulfuric acid is consumed and water is formed, reducing the density of the acid.
This reaction can be written:
PbO2 + Pb + 2 H2 SO4 → 2 PbSO4 + 2 H2 O