A cell contains chemicals that react to produce electricity. A simple cell can be made by connecting two different metals, called electrodes, so that both are in contact with an electrolyte. The electrolyte is a solution that contains ions, such as salt water or dilute acid.
The voltage a cell produces depends on the type of electrode and the type of electrolyte. For two different metals in the same electrolyte, the bigger the difference in reactivity between the metals, the bigger the voltage. A magnesium and copper cell therefore gives a higher voltage than a zinc and copper cell, because magnesium is further from copper in the reactivity series. Two electrodes made of the same metal give no voltage.
A battery is two or more cells connected together in series. Connecting cells in series gives a greater voltage than a single cell.
In a non-rechargeable cell or battery the chemical reactions stop when one of the reactants has been used up, and the battery is then flat. Alkaline batteries are non-rechargeable. In a rechargeable cell or battery the reactions can be reversed by supplying an external electrical current, so the battery can be recharged and used again.