VRLA battery failure mechanism in field applications

Valve-regulated lead acid (VRLA) batteries have been deployed widely as backup energy reserve for telecommunication applications, particularly in outdoor installations. Two issues have been raised for the VRLA batteries in these uncontrolled environments, namely, thermal runaway and excessive hydrogen gassing. In this work, a battery aging process is proposed to show that a large number of shorted batteries (zero float voltage) is unlikely during thermal runaway of a string of batteries. Failure analysis of field batteries and laboratory polarization results are presented. In thermal aging, the internal resistance was found to increase and will impact the amount of float current that can be passed through the string. The float current can only reach a limiting value and drop with increasing internal resistance.