Abstract: The interface between the plastic cover of a battery container and the lead or other metal terminal post which extends therethrough is sealed with a rubber bushing which is compressed and extruded along the terminal post during installation and locked tightly in its compressed and extruded state. The bushing preferably has a pair of oppositely angled intersecting frustoconical surfaces on its exterior surface which are adapted to cooperate with mating surfaces surrounding the opening in the cover and on a locking retainer. The assembly provides a flexible seal which will accommodate the inevitable vertical movement of the terminal post as a result of battery element expansion. Most importantly, the assembly provides an extremely effective barrier to the migration of electrolyte along the terminal post to prevent outer terminal corrosion.