corroded battery cover no longer makes connection
Olin is correct - but it can be hard in practice and may result in destruction of what is left.

Ideas only:


Shim brass may work well for you - brass sheet is available in thickness of a few thousands of an inch up. Wrapping a sleeve or "U" of suitably thin brass over the dead contact metal should work. 
You can get aluminum foil that is much solider than what is sold for food wrap. And, failing in  in time and needing replacing seems preferable to the alternative.
You can buy conductive epoxies, which are often just "ordinary" epoxy loaded with a conductive material - perhaps copper, perhaps carbon black. You can probably make your own by experimenting. Copper filings and epoxy a good starting point. My experience with similar (lacquer loaded with silver for flexible PC  track repair, is that you can get connections which do not work but they improve as the epoxy sets. You need pressure on the grains to make a contact to conduct.
Ask your local industrial chemical suppliers about "Wood's metal". This melts at about 70oC so can be melted with hot water then poured onto the contact area. I have no experience with this - it may or may not work in this application.


Wood's metal is useful as a low-melting solder, low-temperature casting metal, ...


Other uses include making custom-shaped apertures and blocks (for example, electron-beam cutouts and lung blocks) for medical radiation treatment, and making metal inlays in wood.

Wood's metal is also useful for repairing antiques. For example, a bent piece of sheet metal may be repaired by casting a Wood's metal die. The low melting temperature of Wood's metal makes it unlikely this will harm the original. The damaged piece can then be clamped in the die and slowly tightened to form it back into shape.


Wood's metal has long been used by model railroad enthusiasts to add weight to locomotives, increasing traction, and the number of cars that can be pulled.




Wood's metal is also used in the making of extracellular electrode for the electro-physiological recording of neural activity.2





Also - unlikely to be a major issue here, but: : Wood's metal is toxic because it contains lead and cadmium, and therefore contact with the bare skin is thought to be harmful, especially in the molten state. Vapor from cadmium-containing alloys is also known to pose a danger to humans