The use of ratiometric measurements to determine battery status

Until the introduction of the valve-regulated Pb-acid (VRLA) cell the typical telecommunication battery system used flooded Pb-acid cells. These required continual monitoring to ensure that the electrolyte levels were maintained and that the specific gravity was within certain limits. When properly maintained, these battery systems were extremely reliable and had an operational life often in excess of twenty years. The short history of the VRLA cell has been somewhat less satisfactory. Introduced to meet a requirement for a battery system that was compact, nonventing and did not require topping up VRLA batteries have been used extensively in remote and unmanned sites. The VRLA battery however has not proved to be as reliable as its predecessors and has been subject to multiple random failures. This paper examines why these failures are occurring and introduces a new technique by which these cell can be monitored and failure modes detected