Behavior of VRLA cells on long term float. II. The effects of temperature, voltage and catalysis on gas evolution and consequent water loss

After more than 18 months on float, production AGM cells continued to emit gas (i.e. lose water) at rates too high to permit a 20 year life. The rates did not appear to be declining with time. Gel cells on the same test, but at a lower float voltage, had lower gas emission rates. Catalysts placed in the gas space of AGM cells reduced gas evolution very significantly, mainly by keeping the negative plates from discharging. In a second experiment the effects of voltage and temperature were studied in more detail, both, with and without catalysts. The results indicate that AGM cells in their present form are ill suited to high temperature applications. The effects of catalysts in AGM cells gave very encouraging results: a reduction in float current, an increase in negative polarization, a lowering of positive polarization, a reduction in gas emissions by a factor of 2 or more, and the ability to float safely at lower voltages with consequent beneficial effect on positive grid corrosion and growth. Our results point to the conclusion that a central problem with VRLA cells in general, and our AGM test cells in particular, is that their negative plates tend to discharge, even on steady-state float, due to the oxygen cycle itself