1. VRLA BATTERIES-FAILURE MODES Sulphation: Negative Plates Corrosion: (a) Negative top- lead corrosion (b) Positive Grid Corrosion Dry-Out/Water-Loss Thermal Runaway/Heat Generation

2. BATTERY FAILURE PREDICTION THE IMPEDANCE METHOD Definition: Any device through which an electrical current will flow exhibits an impedance to that flow Significant research in cell impedance has demonstrated a proportional relationship with cell age and discharge history Cells of similar size, age and manufacture consistently exhibit similar AC Impedance readings until cell conditions deteriorate. A cell in poor condition because of sulphating plates or deficient internal connections displays a higher than normal impedance.

3. BATTERY FAILURE PREDICTION THE IMPEDANCE METHOD By testing the capacity & impedance of new cells, baseline data can be established Baseline data will vary, according to cell size and manufacturer, but individual cell condition can be determined by comparing the impedance value against its baseline. This technique can also be used to highlight problem cells in a battery bank. Good cells exhibit a similar impedance value. 30% deviation indicates problem cells.

4. Impedance as a function of cell life