Battery (All): Terminology: Electrolyte
In a lead battery, electrolyte consists of concentrated sulfuric acid and distilled water. Electrolyte is a liquid that conducts current and adds hydrogen and sulfate ions to the electro-chemical reaction during charging and discharging:
PbO2 + Pb + 2 H2 SO4 = 2 PbSO4 + 2 H2 O