Internal Resistance: Harbinger of Capacity Loss in Starved Electrolyte Sealed Lead Acid Batteries

In many standby applications, the battery technology of choice is lead acid. Where the application is critical the state of health of the battery is a primary concern. A simple evaluaton technique for determining the battery's performance would be highly desirable. Described are measurements of battery impedance made on a sealed lead acid battery of a particular type. At least one important failure mechanism, dryout, is usefully presaged by an increase in impedance of sealed lead acid batteries. The impedance rise, which is observed to be log-linear with time on float, is accompanied by a linear loss of cell weight due to water loss. The results suggest that battery impedance may provide a useful diagnostic for sealed lead acid batteries if simple calibration experiments are performed on cells of the type to be monitored.