Expanders an an essential component of lead/acid batteries. They prevent performance losses in negative plates that would otherwise be caused by passivation and structural changes in the active material. The functions of the components of modern negative-plate expanders are described and data are presented to show how the capacity and life of the battery are affected by the type and amount of barium sulfate and lignin incorporated in the expander blend. The differences between expanders for automotive, deep-cycle and standby-power batteries are illustrated and typical formulations shown for each application. There are several ways in which expanders can be incorporated into negative plates. These range from adding the individual components to the paste mix to adding a pre-blended formulation. The benefits of pre-blending are more uniform distribution of expander in the plate, simplification of paste mixing, and improved quality control.