The lead-acid battery continues to be the battery of choice for traction applications. Golf carts, lift-trucks and automatic guided vehicles are only a few of the traction-related markets which depend on the lead-acid battery for their continued growth and success. Throughout the world, traction battery manufacturers use a wide range of grid designs, grid alloys, paste formulations, separators and other features to optimize the deep-cycle performance of their products. In this complex array of design features, the least understood parameter is most likely the battery separator. Though somewhat inconspicuous by nature, the traction-battery separator can, if properly selected, play a key role in performance, by extending the life of both the positive and negative plates while at the same time reducing battery maintenance and power requirements for recharging. This paper discusses the various design features of a battery separator and describes how such features may be used to effect the performance and life of the traction battery. Separator porosity, material composition, backweb thickness, rib dimensions and the use of attached glass mats are some of the controlled variables.