Additives to lead–acid battery active materials and components are categorized as physical and chemical attribute additives. Separators are equally divided into two classes, those that have inner skeletal structures, commonly made of mixtures of polymers and precipitated silica, and those that are made of loose fibers. Separator additives are also briefly discussed. Both physical and chemical impacts of active material additives on separators are considered. With the noted exception of negative plate expanders, very little interaction has been reported thus far between active material additives and separators. This question should be further investigated in the light of the growing importance of additives in improving the performance of the lead–acid battery.