1- Get a 5000 grit automotive sanding pad (available at any auto parts store) and hit the silver contact where it makes contact with the battery then wipe it down with alcohol. You can see the little carbonization/black spot starting there in your pic. Thanks to Russ for that tip.
NOOOOOOOOO!!!
Use a soft, white pencil eraser to polish and buff silver.
Tapatyped
and enjoying a tasty beverage. My two favorite things!!