Investigation and analysis of premature failure of valve regulated lead acid batteries

Abstract

Over the past fifty years Valve Regulated Lead Acid (VRLA) battery has been deployed with Uninterruptable Power Supplies (UPS) backup systems as a last line of defense against primary power outages, due to its affordability and maintainability. Although other newer battery technologies such as Lithium-Ion and Sodium Nickel Chloride are starting to take more space in the market, most of the safety-critical systems still depend on VRLA batteries for energy storage. The usage of VRLA batteries with UPS backup systems continues to increase, although up to 40% of VRLA cells fail prematurely. This high failure rate compromises safety and it is also a substantial loss of revenue. The charging and discharging method on a battery is very crucial because it can affect the life span of a battery. When a lead-acid battery is discharging or charging, lead-sulfate crystals build up gradually on the electrodes, this could result in total loss of capacity if a battery is not charged properly. In this study, a collection of ninety-six VRLA batteries based on GEL electrolyte and Absorbent Glass Matt (AGM) type were tested under float and cyclic applications. The battery strings were arranged in a series connection of 32 VRLA batteries at three different test sites. The specification of battery strings used is based on ampere-hour and voltage ratings of 170 AH and 12 V respectively. The batteries were continuously monitored for more than 600 days using Sentinel Battery Monitoring System (BMS) and the performance data were analyzed to identify the rate of premature failure. The result obtained shows that VRLA batteries that are based on GEL electrolyte are more robust than those that are based on AGM technology. One battery out of thirty-two GEL electrolyte type batteries failed as compared to thirty-two batteries out of sixty-four AGM type batteries that failed within twenty-four months. It was also observed that the GEL type is more suitable for cyclic application, whereas AGM is more suitable for float application. In addition, it was also observed that the equalization charge proved to improve the life cycle of both types of VRLA batteries.