Internal Resistance: Harbinger of Premature Capacity Loss in Starved-Electrolyte, Lead-Free Batteries

Starved electrolyte sealed lead-acid batteries (SESLAB's) promise maintenance-free operation in any orientation, but, because the electrolyte is absorbed within a felt material, are not amenable to the inspection and maintenance procedures that have been developed for flooded cells. Consequently, of major concern in standby power application is the reliability of SESLAB's. We have discovered that at least one important failure mechanism, dry out, is usefully presaged by an increase in the internal resistance of SESLAB's. The resistance 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. Our results with one particular cell geometry suggest that cell resistance may provide a useful diagnostic for SESLAB's if simple calibration experiments are performed on cells of the type to be monitored.