Valve-regulated lead/acid (VRLA) batteries provide the very high level
s of reliability required for stand-by service. Various types are avai
lable and, in particular, cells with lead-calcium-tin alloy grids and
absorptive glass-mat (AGM) separators, cells with pure-lead grids and
AGM separators, and cells with tubular plates and gelled electrolyte.
The cell types are subject to a number of factors that affect durabili
ty in floating service. The factors are reviewed and it is shown that
grid corrosion is the usual failure mode. As a result, practical cell
and battery designs need to ensure that all other potential causes of
failure are either eliminated or occur at a slower rate. Test results
based on thermal acceleration are presented and have been correlated w
ith real-time tests. The attainment of satisfactory product life under
practical conditions is fully demonstrated. Techniques for battery mo
nitoring and surveillance also have a strong impact on reliability and
can be used to define the best strategy for replacement. The overall
result is better levels of protection which, together with precise spe
cification and careful consideration of the service conditions, enable
user requirements to be met in full.