An investigation into the effect of abuse charging and thermal runaway in VRLA batteries

VRLA batteries were subject to abuse charging at potentials of up to 2.65 V per cell and ambient temperatures up to 60°C. The current and temperature were monitored for each thermal runaway event. In some experiments the gassing rate was also measured. Both new and old batteries were used. It was concluded that the main cause of batteries going into thermal runaway was the applied voltage, temperature having only a secondary influence. A theory was proposed to explain the results. In all experiments the batteries failed safe.