The ER of a battery separator is a standard measurement used by separator and battery manufacturers for quality control purposes and separator selection.

Separator ER and the separator'interaction with the electrolyte, that is resistance to wetting or flow, will contribute to the internal resistance of the battery and this can potentially limit the electrical output of a battery. The ER determination is a tool for battery manufacturers to use in design, material selection, and performance specifications.

The change in the bath electrical resistance imparted by a separator is affected by the porosity, thickness, and tortuousity of the pore structure of the separator, the wettability of the separator to the electrolyte, and the temperature and concentration of the electrolyte.

Incomplete wetting or saturation of the pore structure limits the lowest ER value obtainable from a separator structure. Separators are pretreated to assure that the specimen being tested has been adequately wetted out. A separator that is not fully wetted out (saturated) will give a higher ER.

This test method is intended to give a rapid and repeatable measurement that approximates the change in ER that could happen when the separator is used in a battery.