The lead acid battery consists of Sponge Lead, Lead Peroxide and Dilute Sulphuric Acid.
It contains plates with tiny square blocks. Lead peroxide is used for positive plates, whereas Sponge lead resembles negative plates. Both the plates are dipped in dilute sulphuric acid, and thereby the load is connected externally.
The electrolyte i.e. sulphuric acid contains charged ions of hydrogen (positive charged) and sulphate (negative charged). When the load is started whether it is headlight or starter, the negative ions contained in sulphate moves towards negative plates and the remaining ions form lead sulphate after combining with plate’s active material.
The strength of the electrolyte is reduced as a result of the process, and thereby an electrical insulation is created on the plate containing sulphate. The electrons flow from the negative terminal of the battery via electrical device to the positive terminal of the battery to complete the circuit. The positive electrons are accepted by the positive plates. In this process, two forms of liquid are formed.
- Water – When hydrogen ions come in contact with oxygen contained in the lead oxide.
- Lead sulphate – When sulphuric acid comes in contact with the lead.
The entire process creates the current flow by the movement of ions around the electrolyte, thereby producing electricity. At one point, the cells get discharged reducing the quantity of ions in the electrolyte and reduce the current flow. Low voltage and current flow makes it insufficient to start the vehicle.
The charging-discharging process continues as the battery is used. However, if the battery is kept without using for long, it gets self-discharged. Generally, the self-discharge rate is 1% per day. The self-discharge is affected the by temperature. For instance, with high temperature the rate increases and vice versa.
Electricity is not stored in the battery, and it is the chemical energy that is stored. The charging process reverses the electromechanical reaction and electricity is converted to chemical energy.
In the charging process, the negative ions are created at the negative plates thereby forcing the positive ions to get attracted towards it. The entire process of flow of electrons is reversed making the batteries fully charged.
The battery life depends on many things and drastically reduces its performance or completely deplete. The following are the few main causes that reduce battery life.
- The battery is kept in partially discharged state.
- The battery is often deeply discharged making it less effective for chemical reaction.
- If you keep the battery for charging for longer duration, the battery becomes unusable. When the rate of charging is more than the natural absorption rate, it will break down or boil the electrolyte.
- If the battery is undercharged, the voltage will be sufficient for the operation, but will be insufficient if the battery is fully depleted.