Design And Function: Discharge

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.

Fig 1: Battery Discharge

Courtesy of VOLVO CARS CORPORATION

The process during discharge

Negative plate: Pure lead is converted to lead sulfate
Electrolyte: The sulfuric acid is converted to water
Positive plate: Lead oxide is converted to lead sulfate
Power consuming components.

During discharge, the lead in the negative plate is converted to lead sulfate (PbSO₄ ).

The lead dioxide (PbO₂ ) in the positive plate is also converted to lead sulfate. During the discharge process, sulfuric acid (H₂ SO₄ ) is consumed while water (H₂ O) is created. This reduces the density of the electrolyte.

The density drops throughout the discharge process and can be gauged to determine the condition of the battery. The electrolyte in a fully charged battery has a density of 1.28 g/cm³ . The density of the electrolyte in a fully discharged battery is 1.10 g/cm³ .