Explain the construction & working of Lead acid battery

Container:

It consists of electrodes, electrolyte and water.

Electrodes:

These are positive and negative metal plates. Anode (PbO2) is connected to positive terminal & cathode (Pb) is connected to negative terminal.

Electrolyte:

It is an dilute chemical solution. Sulphuric acid (H2SO4)

Working:

Chemical Changes During Discharging: When a lead acid battery is fully charged the anode and cathode of it’s cells are converted into Lead Peroxide ( PbO2) and Sponge Lead ( Pb ) respectively. During the process of discharge , The current within the cell is moving from cathode to anode , So the Hydrogen ions moves to anode and Sulfate ions moves to the cathode. At Anode, Hydrogen combines with Lead Peroxide and reacts with Sulfuric acid to form Lead Sulfate. or, 

PbO2 + H2 + H2SO4 = PbSO4 + 2H2O 

And at the cathode, the Lead and Sulfate combines to form Lead Sulfate. Or, 

Pb + SO4 = PbSO4 

So, during the discharging of lead acid battery the plates of cells are both converted into Lead Sulfate which is whitish in colour, Due to formation of water the specific gravity of the cells decreases and also the EMF of the cell decreases. 

Chemical Changes During Charging: 
 Explain working of any one type of battery you know.

Now, When the cell is recharged again , The hydrogen ions moves to cathode and Sulfate Ions moves to anode, At cathode , The lead sulfate reacts with Hydrogen to give Lead and Sulfuric acid, Or,

PbSO4 + H2 = Pb + H2SO4 

And at anode the Sulfate reacts with Lead sulfate along with water to give Lead Peroxide and Sulfuric acid. Or, 

PbSO4 + 2H2O + SO4 = PbO2 + 2H2SO4 

So, during the process of recharging the plates gets reverted back into their original conditions, The specific gravity of the cells increases due to formation of Sulfuric acid and the EMF of cells or battery increases.