V40 L4-1.9L Turbo VIN 29 B4204T3 (2002)
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.
Corrosion
Batteries may corrode in hot conditions, particularly in countries with hot climates. At high temperatures, the grille in the cell plates corrodes and
becomes porous. The connections between the plates may also corrode. The result is a reduction in conductivity and therefore capacity.
Vibrations
The battery is subjected to vibrations if the car is driven on uneven surfaces. Such vibrations can place stress on the inner connections in the battery and
cell units, resulting in wear and damage to the battery. This is a rare occurrence in modern cars however.
Terminology
Terminology
AGM-battery
For AGM-batteries, the pocket separator consists of a thin fibre-glass mat (AGM = Absorbed Glass Mat).
See: Separator
Active material
The active material consists of lead oxide in the positive plates and porous lead in the negative plates. The active materials react with the sulfuric acid in
the electrolyte during charging and discharging according to the following chemical reaction:
PbO2 + Pb + 2 H2SO4 = 2 PbSO4 + 2 H2O
Ampere (A)
Unit for electrical current. Abbreviated to A.
Ampere hours (Ah)
Unit of measurement used to measure the ability of the battery to store electricity or the capacity. The storage capacity is obtained by multiplying the
outflowing current in amperes by the discharge time in hours. Ampere hours are abbreviated to Ah.
Example:
A battery that supplies 3 amperes for 20 hours provides 3 A x 20 h = 60 Ah.
