Battery (All): Terminology: Electrolyte
WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
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