Battery (All): Terminology: Electrolyte
WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
In a lead battery, electrolyte consists of concentrated sulphuric acid and distilled water. Electrolyte is a liquid that conducts current and adds hydrogen and sulphate ions to the electro-chemical reaction during charging and discharging:
PbO2 + Pb + 2 H2 SO4 = 2 PbSO4 + 2 H2 O