A storage battery can have a relatively long life. Some lead acid batteries may operate efficiently for around 20 years or more, provided all conditions of operation are ideal. Such conditions are not usually obtainable.
The end of battery life may result from either loss of active material, lack of contact of active material with conducting parts, or failure of insulation i.e. separators. These conditions may arise in a number of ways. The following are some common causes and results of deterioration of lead acid battery:
Overcharging
If a battery is charged in excess of what is required, following harmful effects will occur:
- A gas is formed which will tend to scrub the active material from the plates. This formation of gas is due to the breakdown of the water in the electrolyte, thus excessive over-charging will lower the water level.
- Overcharging aggravates plate buckling and warping, resulting in damage to the separators.
Undercharging
If a battery is operated with insufficient charge for a long period of time, the following harmful effects will occur.
- Sulphation of the plates. Sulphation results in buckling of the plates, a reduction in specific gravity and a formation of metallic lead in the separators.
- Freezing is more likely to occur when specific gravity is low.
- A battery in an undercharged condition is unable to deliver full power.
Local Galvanic Action
Local Galvanic Action refers to local electrolytic action between the grid and active material of the same plate. Excessive local action will cause a release of hydrogen gas from the negative plates on open circuit and will result in a reduction of final charge voltage. If local galvanic action is uniform throughout the battery, no serious effect will be noted in the battery performance. The charging current required will be increased which may reduce the life of the positive plates. However, if local action is confined to only a few cells, a troublesome condition may exist, their floating voltage will be lower, indicating that they are not getting enough charge. The floating voltage of the entire battery must then be raised, which will result in overcharging the cells that have no defect. The only remedy is to charge the weak cells separately.
Loss of Active Material
This is due to successive expansion and contraction on charge and discharge. This action increases with the amount of working to which the cell is subjected and may be the limiting factor in cell life when working is considerable as in automotive units. An indication of loss of active material from the plates is shown in the amount of sediment at the bottom of the cell.
Excessive Rate of Charge or Discharge
Excessive rate of charge or discharge will result in battery deterioration by producing damaging high temperatures.
Electrolytic Action
This effect takes place due to the action of the electrolyte in contact with the grid of the positive plate. In a worked battery, this electrolytic action is not serious, providing the effect is not localized. Such local attacks are indicated by cracked grid frames which may eventually result in the plate breaking apart.
Entrance of Impurities
This is most likely to occur through water added to the electrolyte. The results of impurity varies with the character of the impurity but usually the result is to aggravate local galvanic action.
Low Water Level
Water must be added to a battery at regular intervals. Damage to the cells will occur if water is not replaced. The acid concentration will increase and eventually disintegrate the wood separators. Therefore the operation of the plates will be permanently impaired.
The effect of local galvanic action is increased as a result of low water and will reduce the final voltage of the affected cells. Water should be added before charging so that it will be thoroughly mixed with the acid by the gassing action during charging.