Continuous charges are also called current (or moving electrons). They are produced by a device called ‘a cell’.

Types of Cells

There are two types of cells. Namely:

1. Primary cells
2. Secondary cells.

A. Primary cells:

These are cells that cannot be recharged once they run down. E.g. torch batteries, calculator batteries, leclanche cell, Daniel cell. The components of the cell are shown

However, primary cells have two defects. They are:

1. Polarization: This is a defect that results from the production of hydrogen bubbles around the copper plate of the cell. This will set up a back emf that reduces the emf in the external. As the cell works, hydrogen bubbles are released. These bubbles insulate the positive electrode and then slow it down. It could be minimized by brushing the plate or by using a depolarizer called manganese (iv) oxide (MnO2), Potassium tetraoxomanganese(IV) KMnO¬, Potassium Heptaoxodichromate (VI) K₂Cr₂O₇… to oxidize the hydrogen bubbles to  form water.
2. Local Action: This defect results from not using a pure zinc plate which makes it to wear It is reduced by amalgamation i.e cleaning the zinc plate with H₂SO₄ and then rubbing it with mercury.

B. Secondary cells:

These are cells that could be recharged when they run down using a suitable battery charger. The two major types are lead acid accumulator and the nickel cadmium cell. E.g car batteries, motorcycle batteries, cell phone batteries and all other  rechargeable batteries.

Difference Between Primary Cell and Secondary Cell
Primary Cell	Secondary Cell
Slow discharge rate and have a high energy density.	Have a smaller energy density
It has high internal resistance	Low internal resistance
Dry cell because it has no fluid inside	There are made up of wet cells (flooded and liquid cells) and molten salt (liquid cells with different composition)
It has an irreversible chemical reaction	It has a reversible chemical reaction
Comes in a smaller and lighter design	More heavier and complex design
Its initial cost is cheap	Its initial cost is high