Field and laboratory studies to assess the state of health of valve-regulated lead acid batteries. I Conductance/capacity correlation studies

Approximately 500 valve-regulated lead acid (VRLA) cells have been capacity tested, and measurements of conductance as well as conventional diagnostic parameters, such as float voltage and specific gravity, have been taken. Cells studied ranged from four to six years´ service, from 200 to 1000 Ah in size and included a group of 6 V 200-Ah monoblocs. Although individual cell capacities ranged from 0% to 100%, there was essentially no correlation of capacity with the conventional diagnostic parameters of float voltage or specific gravity. By contrast, correlation of conductance with capacity was universally high, and sufficiently good to allow statistical prediction of capacity to be made from individual cell conductance values. Limited temperature test data, measured during discharge, show a significantly greater increase than would be expected in a vented (flooded) cell, of similar size and at similar rates. Additional data are needed to quantify this effect and determine necessary temperature correction factors for capacity discharge tests of VRLA cells