Performance of flooded- and gelled-electrolyte lead/acid batteries under remote-area power-supply duty

Both flooded-electrolyte and gelled-electrolyte lead/acid batteries have been operated under field and simulated remote-area power-supply (RAPS) service. Suitably designed batteries of the flat-plate, flooded-electrolyte variety provide the best performance under laboratory conditions. Good results can also be obtained from tubular-plate, flooded-electrolyte units, as well as from flat- and tubular-plate gelled-electrolyte types. Operation at elevated temperatures reduces the lifetime of both the gelled-electrolyte and the tubular-plate, flooded-electrolyte batteries. The principal failure modes of flooded-electrolyte batteries operated at moderate temperatures are degradation of the positive active-material (i.e., shedding, sulfation) and corrosion of the positive grid. At higher temperatures, grid corrosion becomes the dominant life-limiting factor. Similar debilitating processes are suffered by gelled-electrolyte batteries. The two best gelled-electrolyte designs identified in the laboratory study have been installed at RAPS sites and have provided 'trouble-free' service for over three years. Also, it has been demonstrated, in both the laboratory and the field, that water loss from gelled-electrolyte batteries does not cause premature failure unless the batteries are excessively overcharged. Thus, it has been confirmed that gelled-electrolyte technology is suitable for use in RAPS facilities, provided that adequate charge control is available. The evaluation programme has identified a set of design and performance specifications for RAPS batteries - the incorporation of these features will relieve many of the failure modes associated with RAPS batteries. In particular, suppression of positive-plate degradation by the application of significant plate-group compression has been identified as crucial for extending battery life under RAPS duty. The specifications have been used to design and construct a series of advanced gelled-electrolyte RAPS batteries. The units are superior to existing commercial gelled-electrolyte batteries when operated at 45 degrees C under simulated RAPS conditions. Finally, an operational strategy for use with batteries that are not prone to acid stratification has been identified. The procedure, termed the 'partial-state-of-charge profile', can provide a three-fold increase in the total energy available from a battery and can yield charging efficiencies of up to 99.5%.