In this paper, we examine the influence of different aspect ratio paste additives on the performance of lead-acid batteries. Previous computer models have been developed to investigate the influence that spherical conductive and non-conductive paste additives have on battery performance. However, many additives used in both the positive and negative plates have aspect ratios that are not spherical. We extend models previously developed for spherical additives to handle additives having different aspect ratios and find that conductive additives with high aspect ratios can improve paste utilization above that of an equal volume of spherical additives. These results suggest that very high aspect ratio conductive additives would be advantageous in improving conductivity in both the negative and positive paste. (C) 2004 Elsevier B.V. All rights reserved.