For the past seven years, Midtronics has developed and manufactured battery conductance testers for determining the condition of automotive batteries. This paper presents a further refinement of the technology. Studies by automobile manufacturers, automotive battery manufacturers, as well as testing by Midtronics and an independent test laboratory have established the utility of conductance technology in evaluating the condition of automotive batteries, even at very low states-of-charge. The use of conductance to determine the state-of-health of stand-by batteries has attracted increasing worldwide interest among both battery manufacturers and users. Attention has focused first on the area of valve-regulated lead/acid batteries (VRBs) for which there are no reliable diagnostics other than a cumbersome discharge test. Several recent studies have demonstrated the validity of conductance testing as an accurate predictor of battery capacity in railroad, electric power utility, stand-by power and telecommunications applications. Other benefits includes: (i) for the first time, tests have resulted in the accumulation and publication of large quantities of actual capacity data for individual valve-regulated cells and batteries that will serve as a standard against which conductance results can be compared; (ii) results of these capacity tests have shown both unusually wide-spread capacity variation and significant numbers of premature capacity failures in valve-regulated cells over a wide range of applications in telecommunications, UPS, photovoltaic and railroad signaling systems; these failures have appeared to occur without regard to specific manufacturers, design, application or use environment; (iii) in addition, both users and manufacturers have generally become more knowledgeable of performance characteristics, ageing mechanisms and failure modes of valve-regulated cells, so that it is now clearly recognized that the number of serious failure modes significantly exceeds those of conventional flooded cells; it has also been recognized that, in almost every case, these same failure modes also affect the cell conductance, this strengthens the logic for the use of conductance as a suitable diagnostic technique. An overview is given of conductance/capacity test results obtained and reported in the last two years, augmented by significant new results, as well as significant new developments in both the instrumentation and application of conductance testing to determine the 'state-of-health' of batteries that range from small 12-V automotive designs to stationary designs as large as 1000 Ah in strings with voltages as high 380 V.
