Some design aspects and the role of AGM separator in VRLA batteries

Valve regulated lead acid batteries (VRLA) have continued to find acceptance in the marketplace. However, over the past few years premature performance shortfall (PPS) has tarnished the image of these batteries. While no manufacturer has been immune from this condition it appears to have affected some manufacturers more than others. It is generally believed that PPS is due to either a loss of water from the electrolyte or is associated with the mechanical instability of the AGM (absorbent glass mat) separator. Several independent tests on commercially available batteries were made in an effort to investigate simulated dry-out conditions, i.e., the same conditions that are presumed to promote PPS. The parameters investigated in these tests include differing electrolyte and sulfate levels as well as tests on the mechanical properties of the acid wetted AGM separator. A final test suggests the importance of proper charging towards maintaining capacity. None of the simulated conditions could initiate PPS in the battery. When properly designed, the AGM mat is found to retain adequate resiliency. The test results suggest that PPS may be primarily attributed to mechanical battery design factors. A generic problem of separator shrinkage causing PPS in VRLA batteries made with AGM mat could not be detected.