Another tip for cleaning - if you get the deep crud off, try rubbing the contacts with a good old-fashioned rubber pencil eraser. It will do a great job on polishing the contacts without undue abrasion. If one of the contacts is a coiled spring, this is a bit tougher to work. They also used to sell little fiberglass contact brushes in camera stores for cleaning battery contacts. You might have to go to Radio Shack to find them now. They'll look like a mechanical pencil with a twist-action to extend the brush head.