Batteries And Cells


  • Storage batteries store electrical energy due to the chemical action taking place between electrodes and electrolytic solution.
  • The smallest element of a battery is a cell. A cell is defined as a source of emf in which chemical energy is converted into electrical energy.
  • The valve of emf produce by a cell depends on :

1. Material used for the plates or electrodes.

2. Types  of  electrolyte.

2. Battery

  • A battery is a group of cells . Depending on the voltage and current requirements, the cell are suitably connected in series parallel configurations.
  • The batteries  give out electrical energy due to chemical reaction taking place, while discharging.
  • During the charging process, the batteries chemical changes take place, which absorb the energy.
  • Thus batteries absorb electrical energy at the time of charging and release it at the time of discharging.
  • A battery consists of a number of cells connected in series to deliver the required output voltage. (say 6V or 12V or 24,48,72 volts)

3. Classification of Cells:

  • The cells are classified into two categories:

1. Primary cells

2. Secondary cells

3.1. Primary cells

  • The chemical action taking place in the primary cells is irreversible. Hence once the terminal voltage goes down, we have to place the primary cell by a new one.
  • The best example of primary cells is the dry cells available in market which are used for radio, walkman, calculators etc.
  • The energy producing capacity of primary cells is limited.
  • Examples of primary cells are alkaline cells, mercury cells, zine-chloride cells etc.

3.2. Secondary cells:

  • The chemical action taking place in the secondary cells is reversible. So it is possible to recharge the cell if it is in the discharge state.
  • In the charging process we have to pass a charging current through the cell in the direction to that of the discharging current.
  • The electrical energy is stored in the form of chemical form, when the charging current is passed.
  • Secondary cells are capable of producing large amount of energy.
  • Examples of secondary cells are lead-acid cells, nickel cadmium alkaline cells.
  • The secondary cells are also called as storage cells or dischargeable cells.
  • There are different type of secondary cells. The commonly used ones are:

1. Lead-acid cell.

2. Nickel iron alkaline cell.

3. Nickel cadmium-alkaline cell.         

4. The Lead Acid Cell:


The construction of lead acid battery cell is an shown in figure 01. This cell consist of the following parts:

Battery cell

1. Anode or positive plate

2. Cathode or negative terminal

3. Electrolyte

4. Separators

5. Container

4.1. Positive plates:The positive plates are also called as anode. The material used for this is lead peroxide (PbO2). It is the material of dark brown colour.

4.2. Negative Plates: The negative plates are also called as cathode. The material used for the cathode is lead (Pb) and its colour its gray. The positive and negative plates are arranged in groups. Positive plates are placed between negative plate. These positive plates are connected together by a connector strap and positive terminal is brought out.

4.3. Electrolyte Used: The electrolyte used is dilute sulphuric acid (H2SO4) with 3-parts of distilled water mixed with one part of H2SO4. The specific gravity is 1.2. The anode and cathode both are immersed in the electrolyte.

4.4. Separators: These are thin plates of porous insulated material like rubber. These are placed between main plates to avoid short circuit amongst themselves. The main plates are placed close to reduce the internal resistance.

4.5. Container: The container is made up of plastic or ceramic. All plates and electrolyte is placed in it. No chemical action should take place on the container.

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