The fluid-transfer properties of the separator play a critical role in both acid- and alkaline-based batteries. These properties are of particular importance in a lead–acid battery since the sulfuric acid is an active component of the battery reaction; the acid is depleted as the battery discharges. In a flooded lead–acid, the function of the separator to deliver acid is less significant than in a valve-regulated design. This paper discusses some issues with regards to this important interaction.