The battery life depends on the operating conditions and the effective maintenance practices followed for regular checking of battery health. The useful life of the lead acid battery can be achieved up to its guaranteed life if the charging and discharging cycles of the battery are as per the ideal operating procedure.
The major reasons for battery failures or reduced battery life are loss of active material, insulation failure of the separator, and damage to the connection points of the battery due to rapid oxidation.
Performance Factors for Battery Life
The following reasons generally contribute to the reduction of the useful life of the battery.
- Discharge Depth
- Local Galvanic Action
- Loss of Active Material
- Excessive Rate of Charging
- Electrolytic action
- Entrance of Impurities
- Low Water Level
Overcharging Reduce Battery Life
The battery charging equation is given below.
During the charging process lead sulfate converts into active material at anode and cathode. The oxygen(O2) gas is liberated at the anode and the hydrogen(H2) gas is liberated at the cathode when the battery is about to charge. If the battery is charged above its capacity, the following pernicious effects will happen.
- The gas formation during overcharging causes water to break down into hydrogen and oxygen gas. The gas formed interacts with the active material and scrub the active material. As a result, the battery charging and discharging capacity deteriorate for the next cycles.
- Excessive charging reduces the water level of the battery. Rapidly lowering the water level in the battery indicates battery overcharging.
- The overcharging of the battery causes excessive heat inside the battery. The extreme heat can cause buckling and wrapping which may eventually cause damage to the separators.
If the battery is not fully charged, it can not deliver the rated amperage to the load, the sulphation formation on the plates is likely to occur because the specific gravity of the battery is low. The discharge equation of the lead acid battery is given below.
If the battery is charged under its capacity, the following adverse effects happen.
- The white material forming on the plate is called Sulphation of the plates. Sulphation can cause the bending( buckling) of the plates and the formation of metallic lead in the separator.
- A battery can not deliver the rated amperage to load if the battery is undercharged.
Discharge Depth Affects Battery Life
The depth of battery discharge adversely affects the life of lead-acid batteries. The depth of discharge means the extent to which battery discharge stops. 80 % depth indicates the release of 80 % stored energy and 100 % depth shows the release of the full capacity of the battery.
The design parameters like deep cycle use, shallow cycle, and floating use are considered during the battery’s design stage. The shallow or floating batteries must be used for specified applications, if they are used for deep cycle applications the batteries are likely to fail.
The deeper discharge depth cause shorter battery cycle life. The lead sulfate is generated during battery discharge and at the time of charging the lead sulfate returns to lead dioxide.
The molar volume of lead sulfide is more than the volume of lead oxide. When one mole of lead oxide converts into lead sulfide, the volume increase by 95%. Repeated charging and discharging of the battery slowly lose the bond between the lead dioxide particles.
The loose bond between PbO2 leads easily dislodgement of particles. The reduction in the active material cause reduction in the charging capacity and thus, adversely affects the useful life of the battery.
Local Galvanic Action affects battery life
If the local galvanic action is formed in the entire battery, more charging current is required to boost the battery voltage. Excessive charging reduces the useful life of the battery. If the local galvanic action forms in a particular cell of the battery, overcharging the battery will not boost the battery voltage. The only solution in this case is charging such a battery separately.
Loss of Active Material
The loss of the active material can be seen as sediment in the bottom of the battery. If the active material loss occurs, the battery will draw more current for charging, and the ampere-hour capacity of the battery gets lowered. After the substantial loss of active material from the plates of the battery, the battery life gets lowered and the battery must be replaced.
Excessive Rate of Charge or Discharge
The battery must be charged and discharged according to the design rating of the battery. Excessive charging and discharging cause heat inside the battery which may damage the plates and separator.
The electrolytic action takes place when the electrolyte comes in contact with the grid of the positive plate. This can cause cracks in the grid frames and further, it may break the plate apart.
Entrance of Impurities
The water added to the battery to maintain the specific gravity of the cell must be free from impurities. The impurity in the distilled water may cause local galvanic action.
Low Water Level
The water level in the battery must be maintained up to the marked level on the battery. The more acid concentration may damage the separators of battery cells and it can permanently damage the battery. The local galvanic action aggravates the low water level in the battery and finally, it will reduce the battery voltage.
Effect of Temperature
The battery capacity increases with the temperature increase because of decreased internal resistance. The performance of the battery increases by 12% at an elevated temperature of 50°C. However, if the battery is operated at a high temperature above 50°C for a longer period of time, it affects the useful life of the battery.