The battery is the main part of the electrical system in an automobile. Without battery, engine cannot be started with the starting motor.
The battery supplies current to various part of the automobile vehicle such as for starting motor, ignition system, head and tail light, brake light, to wiper and other accessories.

A car battery is a rechargeable battery used to jump start a motor vehicle. Its primary purpose is to provide an electrical current to the electric starter motor, which in turn ignites the chemically powered internal combustion engine that actually drives the vehicle.


The type of batteries are
1) Lead-Acid battery
2) Alkaline battery
This is also two type
a) Nickel iron type
b) Nickel cadmium type

3) Zinc-air battery

Vehicle batteries should be robust construction since they are are to withstand sever vibration in addition to the high charging rate as well as heavy discharge convent required for different automobile service.
The construction with component of lead acid battery is explain below.

Function of Battery

  1. Battery supply high current to starter motor and low current to ignition system.
  2. It supplies current to accessories which operate electrically.
  3. Without Battery Engine Wont Fire
  4. It stores the electrical energy and control the voltage regulation of electrical system.
  5. Works With The Alternator to Power Electronics
  6. The battery helps regulate voltage

Lead-Acid battery



The lead acid battery is widely used in automobile vehicle.
It consist of following component –

1) Container

It is constructed in single piece and made of acid resistance of hard rubber or plastic or bituminous composition.
It is divided by partitions into compartments for individual cell.
Ribs are there at the button of each compartment. The battery plates rest on these ribs.
The space between the ribs are provided to collect sediments. This minimizes the danger of short circuit due to sediment.

2) Grids and Plates

The battery plates are made of a lead alloy containing 6 to 8% antimony, which makes them resistant to electrochemical corrosion and gives them a strength and rigidity.
The plates are in the form of grids. Number of plates of positive and negative types and separators are there in a cell. Positive plates are kept one less than the negative plate in order to make use of all surface of the positive plate.
On the plate grids, lead oxide paste is applied. Then plates are assembled into a battery.
The cells are filled with electrolyte and given an initial charge.
This changes the lead oxide paste on the negative plate to sponge lead which is grey in colour and changes the lead oxide paste on the positive plate to lead peroxide which is brown in colour.
The plates are properly spaced and welded to a lead antimony plate strap. This form a plate group.
Each cell is composed of negative and positive plate group and separator.
The negative and positive plate are arrange alternatively.

3) Separator

Separators are placed between the negative and positive plates. This prevents the positive and negative plates from direct contact with each other,resulting internal short circuit.
Also they may be porous to permit electrolyte to circulate between the plates.
The separator are made of wood, spun glass, porous rubber sheet, glass fibre or resin impregnated fibre, PVC of porous plastic.
Some batteries have separators made of polyvinyl chloride or polyethylene saturated cellulose.
Separators have ribs on the side facing the positive plate provide greater electrolyte volume to next to the positive and improve efficiency by increasing electrolyte circulation.

4) Cell cover

Each cell is sealedby a cover of hard rubber through which the positive and negative terminals are projected.
Adjacent negative and negative terminal are connected by cell connector strap.
It’s cover have an opening for filling the electrolyte and a filler cap is provided on this opening with an air vent to scape the gases.

5) Electrolyte

The sponge lead and lead peroxide which fill the respective plate.
Electrolyte is a chemically pure sulphuric acid diluted with distilled water.
It consists of 40% sulphuric acid and 60% distilled water.
The specific gravity of the electrolyte poured into a new battery with dry charges plate ranges from 1.25 to 1.28 gm/cm3. The level of electrolyte must be 10 to 15 mm above the top of the plate.
When the electrolyte has been added and the battery is given an initial charge then it is ready for operation.

6) Cell connectors

Connector straps connect the negative and positive terminal post of the adjacent cell just above the cell cover.
Each cell of a lead acid battery produce two volts.
Connectors must be heavy enough to carry high current required for starting without overheating.

7) Taper terminals

Battery terminals are of special design made tapered to specified dimension. So that all positive and negative cable clamp will be fit.
The positive terminal are slightly larger in diameter at top than negative terminal.

8) Sealing compound

They are blends of specially processed bituminous substance having resistance to flow at high temperature and resistance to crack at low temperature.

Working of battery

The working of battery can be understood by knowing the charges taking place dining the charging or discharging of the battery.

Chemical reaction during charging and discharging
The chemical reaction takes place between the three chemicals in the battery. In presence of Sulphuric Acid ( H2SO4 ), the electron from one group of plate collect on the other group of plate. This flow of electrons is continue until there is insufficient in balance of electron to create a two volts pressure between two group of plate.

This results in a pressure of 2 volts between the terminals of the battery cell. If two terminals are connected by a circuit the electron will flow. After a certain amount of current has been withdrawn, the battery is discharged or dead. When it is discharged, it is not capable of delivering any aadditional current.It is then charged.

The chemical reaction takes place while the battery is charged and discharged –

PbO2 + 2 H2SO4 + Pb = PbSO4 + 2 H20 + PbSO4 + Q

Lead Peroxide (+) Sulphuric Acid (-) Lead Lead Sulphate (+) Water Lead Sulphate (-) Energy
(Positive plate) (Electrolyte)


During discharging of battery the sulphuric acid (H2SO4) is split into hydrogen (H2) and sulphate (SO4). The hydrogen liberate at the lead oxide (PbO) which combine with part of sulphuric acid to form lead sulphate (PbSO4) and water.

The sulphate is librated at the spongy lead plates (Pb) and combines with them to form lead sulphate (PbSO4). During this process the electrolyte becomes dilute because of the absorption of SO4 by the sponge lead plates.

When battery is charged, the chemical reaction shown above become reverse. The lead sulphate on the plate again convert to lead peroxide and the lead sulphate on other plate is reduced to spongy lead (Pb). Thus the electrolyte become concentrated because of increase in H2SO4.

Thus the battery convert electrical energy into chemical during charging and chemical energy into electrical energy during discharging.
At higher temperature the chemical reaction operates very vigorously while it is very slow at slow at lower temperature.

Rating of battery

The battery rating are recommended by Society of Automotive engineers
1) 20-hours rating ( in ampere hours)
It indicates the lighting ability of a full charges battery. It is obtained the discharging the battery at a current rate equal to 1/20 of the manufacturer’s ampere hour rating. The current rate that battery deliver continuously for 20 hours after which cell voltage should not drop below 1.75 and battery temperature is 80 degree F.

2) Cold rating
It gives an indication of the cold weather starting ability of the battery. The number of minutes of a 6 volt battery can deliver 300 ampere at 0 degree F before cell voltage drop below 1 volt.

3) 25-Ampere rating
It measures the battery performance at a moderate constant current output at 80 degree F to a final limiting voltage 1.75 volt/cell.

4) 20 minute rate
It is the amount of current a battery can delivered continuously dining 20 minute without dropping the cell voltage below 1.5. A temperature of 27 degree C is maintained at the start of the test.

Capacity of battery

The capacity of battery has been defined as the amount of current it can deliver.
The maximum amount of current that a cell can furnish is dependent upon the following factor

a) Number of plates
b) Area of plate
c) Temperature of electrolyte
d) Quantity of electrolyte

About 1/10 m2 of the surface plate must be in contact with an electrolyte to produce 40 to 60 ampere of current. 6 volt passenger car battery have 15-17-19 and 21 plates per cell , the 12 volt have 7- 9- 11 and 13 plates per cell depending upon the size of the battery.
There is always one more negative plate then positive plate.


Which battery is used in automobile?
Lead Acid Battery
The most common type of car battery in India is a Lead Acid Battery. It comprises many plates placed in an electrolyte solution. This solution is made of 65% water and 35% sulphuric acid. The current is produced by the chemical reaction between the plates and the electrolyte solution.

What are the 3 types of batteries?
1) Lead-Acid battery
2) Alkaline battery
3) Zinc-air battery

What is the basic principle of battery?
A battery is a device that stores chemical energy and converts it into electrical energy. Chemical reactions in a battery involve the flow of electrons from one material (electrode) to another, through an external circuit. The flow of electrons provides an electrical current that can be used to do work.

What are the 3 basic components of a battery?
There are three main components of a battery: two terminals made of different chemicals (typically metals), the anode and the cathode; and the electrolyte, which separates these terminals. The electrolyte is a chemical medium that allows the flow of electrical charge between the cathode and the anode.

Which acid is used in battery?
sulfuric acid

Is a car battery AC or DC?

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By Aditya

Hi, I’m Aditya Sharma, a professional blogger from Gurgaon, India and I launched this blog called aadityacademy on July 2021. is a mechanical Project-oriented platform run by Aditya sharma and I got the motivation to start aadityacademy blog after seeing less technical education information available on google.

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