You can clean the battery alkaline leaks with white vinegar on a cotton swab. If the battery was removed shortly after leaking then the amount of alkaline residue should be small and not too much damage to the contacts. The cotton swab should be damp and not dripping wet, the vinegar acids will neutralize the alkaline residues. Be gentle with the contacts but make sure that they are clean and the wires are intact. You can follow the vinegar with isoplyl alcohol to clean up left over residues.