The fundamental theory of the battery is that a voltage is developed between two electrodes of dissimilar metal when they are immersed in an electrolyte. In the typical lead-acid cell the generated voltage is 2.1 volts. A typical 12 volt Lead Acid Battery consists of 6 cells with Lead Dioxide (Positive Plate), Sponge Lead (negative plate) and Sulphuric Acid (H2S04) - electrolyte. In a normal discharge operation the lead reacts with sulphuric acid and become lead sulphate and water. This dilutes electrolyte. During a charging operation the reverse process take place. Watch the figure below to understand the discharge process.
Lead Acid Battery – Discharge Process
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