It is true that the battery "medium" is an alkaline paste. If that has leaked on the contacts then an acid will neutralize the alkalinity but if the paste has dried it may be hard to remove the "crust" or to re-dissolve it. And if the contacts are rusted vinegar or citric acid by themselves may not help to remove it.
My go-to is a solution of 1 part phosphoric acid / three parts hot water. Neutralizes alkali, dissolves crust, reduces rust (oxide) to metal. Leaves a black powder that can be brushed off. I would not try this with the contacts in the case. -CH-
