Typical lead acid batteryThis is a common type of battery used in plant vehicles.

Any two dissimilar metals, when immersed in an electrolyte, will provide a voltage across the two metals. One metal will become more positive, and the other metal will become more negative.

In other words, we now have an electrical potential difference between the two terminals. We can use this potential difference to do work.

In a lead acid battery, the two different metals we use are lead peroxide (the + plate) and pure sponge lead (the - plate). The electrolyte we immerse them in is a dilute solution of sulphuric acid.

This combination of plates and electrolyte will produce a potential difference of 2.2V for each cell.

If we wire 6 cells together in series (a battery of cells), this will give us a potential of 13.2V.

In practice, because of the internal resistance of this arrangement, a fully charged lead acid battery will normally give a reading of approximately 12.8V

You can read more about the structure of lead acid batteries here

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