The effect of VRLA separator saturation on EV battery life

Field and experimental data are used to describe the relationship between the estimated initial separator saturation of VRLA traction batteries and the susceptibility of an EV battery pack to failure under shallow discharge conditions in climates such as that encountered in the southeastern United States. Arguments are made in support of the theory that low or reduced separator saturation leads to escalating oxygen recombination rates in VRLA, which in turn elevates the pack operating temperature and results in increased corrosion and electrolyte dryout. A method to estimate the charge acceptance based on thermal data is also described.