Are you using a
threaded charger or the type that you just push the battery into? If it's the
threaded type, first try cleaning off the battery
threads with a little rubbing alcohol on a scrap of paper towel with some small tool (eyeglass screwdriver, toothpick, whatever) to help push it down in there. If you haven't already, carefully (since it's an auto) clean the battery post and threads in the same way. Let them dry and try again.
Another trick is to take some very fine sandpaper and use it lightly on the threads of the battery by holding the sandpaper on the threads and gently twisting the battery back and forth a few times. Sometimes this helps improve contact with the charger.
Short of that, you either have a bad battery (which can be returned if it's within 45 days of purchase.... I've done it) or a bad charger.
