Battery Information

How does a battery work?

A battery is an electrochemical device. It stores chemical energy which can be released as electrical energy when it is needed.

When two dissimilar metals are immersed in an electrolyte, a battery is created and a voltage is developed.

In a lead acid battery the two unlike metals are:

Lead Dioxide [PbO₂] - for the positive plate

And

Sponge Lead [Pb] - for the negative plate

and the electrolyte is :

Sulphuric Acid [2H₂SO₄] diluted in water [H₂O].

A typical lead acid battery cell produces about 2.1Volts per cell. Therefore a 12Volt battery comprises six cells connected in series. Each cell is made up of several positive plates with an equal number of negative plates, which are interspersed with separators and immersed in electrolyte.

During discharge, electrical energy is released; causing both the negative and positive plates to slowly convert to lead sulphate [PbSO₄] and the electrolyte loses its acidity to become water [2H₂O].

The sulphuric acid [H₂SO₄] combines with the positive plate [PbO₂] converting it to lead sulphate [PbSO₄] and displaces oxygen [O₂] and hydrogen [H₂] which combine to form water [H₂O].

The sulphuric acid [H₂SO₄] combines with the negative plate [Pb] converting it to lead sulphate [PbSO₄] and displaces hydrogen [H₂] which combines with the oxygen [O₂] liberated from the positive plate to form water [H₂O]. Small amounts of hydrogen and oxygen gases are also released.

During charging, the process is reversed. Electrical energy now flows into the battery, the lead sulphate on both plates convert back to lead dioxide and sponge lead.

Other battery chemistries operate using the same basic principles. For example, a Nickel Cadmium [NiCd] battery uses nickel [Ni] on the positive plate and cadmium [Cd] on the negative plate with an alkaline electrolyte and produces 1.2Volts per cell.

Why do batteries stop working?

From the time a battery leaves the factory, it begins to deteriorate, no matter what type of battery it is.

But with proper care, attention and regular exercise, it is possible to prolong the life of the battery so it only stops working due to old age [i.e. it has worn out].

However, most batteries stop working prematurely as a result of:

Short circuit, overloading or electrical system faults.
Overcharging.
Lack of maintenance of the battery and/or the equipment associated with the battery.
Battery is left discharged, or stored at the incorrect level of charge.
Recharging and/or discharging the battery incorrectly. Different battery types have different requirements.
Battery not suitable for its equipment or application.
Please read the topic 'How to get the most from your batteries' to learn more on how to use and care for the different battery types.

For lead acid batteries, incorrect use and lack of maintenance allows 'hard' lead sulphate crystal formation. This accounts for 75% of batteries that have failed.

If a lead acid battery is left discharged for any period of time, the lead sulphate on the plates begins to crystallise. This crystallised [or 'hard'] lead sulphate build-up on the plates cannot be broken down just by re-charging. This in turn reduces the amount of sulphate ions [SO₄] which can return to the electrolyte during re-charging, limiting the amount of charge the battery can store.

The crystallised [or 'hard'] lead sulphate will build up over time [the rate of build-up varies with the way each battery is used, i.e., charged, discharged, stored], gradually reducing its efficiency to the point where it will no longer be able to hold enough charge. It is at this point that the battery is replaced.