The majority of lead acid battery failures can be attributed to degradation of the positive active material. In this paper the results from a study to investigate the effects of adding carbon fibre additive to red lead positive paste are presented. The test batteries manufactured were evaluated using capacity and cycle life tests prior to destructive examination and analysis using scanning electron microscopy and X-ray diffraction. Results suggest the addition of carbon fibre to positive paste increases capacity by approximately 20%. Significant improvements in cycle life were also observed. (C) 2003 Kluwer Academic Publishers.