Analyzing defective lead-acid batteries involves diagnosing the causes of failure or underperformance. Various factors can lead to defects or degradation in lead-acid batteries, including sulfation, grid corrosion, electrolyte loss, and internal short circuits. A thorough analysis often requires examining the physical components of the battery, testing its electrical characteristics, and understanding its usage history.
1. Sulfation
Sulfation occurs when lead sulfate crystals form on the battery plates and are not converted back into active material during charging. It can be caused by prolonged storage without charging, undercharging, or operating the battery at a low state of charge.
- Analysis: Sulfation is often diagnosed through voltage tests and charging behavior. Batteries with severe sulfation may not reach their full voltage when charged or may exhibit rapid self-discharge.
2. Grid Corrosion
Grid corrosion, particularly of the positive grid, leads to the loss of active material and a decrease in the battery’s capacity. It is often accelerated by high temperatures and overcharging.
- Analysis: Visual inspection of the grids (if possible) can reveal corrosion. Also, a decrease in battery capacity or difficulty in reaching full charge can indicate grid corrosion.
3. Electrolyte Loss
Loss of electrolyte can occur due to overcharging, high temperatures, or physical damage to the battery casing. It results in increased concentration of the acid, which can accelerate corrosion and sulfation.
- Analysis: Electrolyte levels can be visually inspected in batteries with removable caps. For sealed batteries, electrolyte loss might be inferred from excessive heating during charging or diminished capacity.
4. Internal Short Circuit
An internal short circuit can occur due to the shedding of active material, which collects at the bottom of the battery and eventually bridges the gap between the plates, or through dendritic growth between the plates.
- Analysis: A battery with an internal short will often have a significantly reduced voltage and capacity. It may also fail to hold a charge or exhibit rapid self-discharge.
5. Defective Cells
Not all cells in a battery may perform equally. A defective or weak cell can drag down the performance of the entire battery.
- Analysis: Individual cell voltages can be measured to identify any cells that are underperforming. Load testing can also help diagnose cells that cannot maintain voltage under load.
