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Fig 1: Identifying Battery Sulfation

Courtesy of VOLVO CARS OF NORTH AMERICA.

Lead sulphate is formed on the plates during discharge. Normally small crystals are formed, which then revert to lead and lead oxide when the battery charges.

In certain circumstances during discharge, large insoluble crystals of lead sulphate may be formed. These crystals may form an insulating layer on the plates. This reduces the effective surface of the plates, reducing the contact between the active materials on the plates and the electrolyte. As a result, the capacity of the battery reduces considerably. This is called sulfation and is a result of a battery being left standing for a long period (in excess of two weeks) at a low charge, or because the battery has been under charged repeatedly.

The plates always expand slightly during discharge. If the discharge is very slow, the expansion may be so great that the plates deform or crack. Such damage is permanent and the battery cannot be used again. If a battery has undergone excessive sulfation, it may be possible to renovate the battery by charging the battery slowly using a very low current.

Regular maintenance charging will prevent sulfation.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Design and function: Sulfation

Use the Manual With the Right Hardware

When to See a Mechanic