This paper outlines some of the improvements in the performance of valve-regulated lead-acid (VRLA) batteries that have been accomplished during the course of the 1990s and considers further advancements which might be achievable. Attention is focused on those aspects of the battery that have been changed in order to convert the original, flooded (vented) design into a valve-regulated unit. Refinements of the components which were modified during the course of the flooded-valve-regulated conversion could be a productive endeavour as research workers strive to raise the life of the VRLA battery to match, and exceed, that of its flooded predecessor. (C) 2000 Elsevier Science S.A. All rights reserved.