Write the cell reaction of a lead storage battery when it is discharged. How does the density of the electrolyte change when the battery is discharged?

 

 
When a lead storage battery is discharged then the following cell reaction takes place 
 
Pb+PbO2+2H2SO42PbSO4+2H2O
 
Density of electrolyte depends upon number of constituent ions present in per unit volume of electrolyte solution. In this case density of electrolyte decreases as water is formed and sulphuric acid is consumed as the product during discharge of the battery.