Section 39 (Electronics - Design And Function - 1 Of 4): Battery: Terminology: Electrolyte
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2013 Volvo C70, 2012 Volvo C70, 2011 Volvo C70, 2010 Volvo C70, and 2009 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