Thermal runaway of VRLA batteries: published test methods versus real life experience

Thermal runaway continues to be a problem in many VRLA battery applications. A test method to verify the propensity for thermal runaway has been published for some time by Bellcore (TR-NWT-000766) as also by another specification (ANSI TI 330-1997). In both, the battery is subjected to progressively increasing voltages and the ensuing temperature and current response analyzed to comment on the propensity for thermal runaway. However, these test methods do not always represent or explain real life incidents. Thus, a combination of exposure to elevated voltage, together with sustained high temperature ambient condition, will increase the danger of thermal runaway. Also, charging (from deep discharge) at high rates and elevated temperature, is yet another prime situation that promotes thermal runaway. Data from special tests to simulate these situations are discussed for possible inclusion in the test procedures.