greasing closed bearings on the outside
Generally speaking, that style of bearing ("sealed cartridge bearing") is "permanently lubricated".  You do not lubricate them and you replace the entire assembly if anything goes wrong with them.  

A few people have claimed success by gently prying back the flexible gasket and injecting grease with a syringe, but these claims are subject to legitimate skepticism.

Note that the inside diameter and the outside diameter are not supposed to move relative to the external parts that hold them.  If they are slipping it indicates that the "holders" are not tight enough or the bearing is failing and needs to be replaced.