A simple lead acid battery consists of positive and negative electrodes Immersed in an electrolyte. The positive electrodes are Pbo₂ (lead oxide) and the negative electrodes are Pb (spongy lead). The electrolyte is dilute sulphuric acid.

On discharging the battery

Pbo₂ + Pb +2 H₂ so₄ →Pbso₄ + Pbso₄ + 2 H₂o

Lead acid is converted into lead sulphate. Spongy lead is also converted into lead sulphate and H₂ so₄ used up in the process. Only water is remain. So the specific gravity of the cell comes down. 

On charging the battery

Pbso₄ + Pbso₄ + 2 H₂o → Pbo₂ + Pb +2 H₂ so₄

Here the products are converted to their original constituents and the acid is released. So the specific gravity rises as the cell is charged. How much ever larger be the cell the voltage of each cell will be approx. 2.15 V when fully charged. 

The positive plate is made of a paste lead oxide, lead sulphate that is fitted in a mesh like material and is connected to grid. All positive plates are made common and connected to a grid. 

The negative plate is made of spongy lead also it is in mesh and connected to grid. These are also grouped together. 

These plates are separated by a micro porous separator for the diffusion of electrolyte. 

The electrolyte is prepared by adding sulphuric acid to distilled water drops by drop and stirring it until the reasoned specific gravity is attained. 

Every thing is placed in a container of hard rubber. The cells of a battery are connected by a cell connector. The container is leak proof.