OK - Brain is finally working. Put a 12v car tail light bulb (enables you to draw about an amp of current) in series with the white lead and hook it to the positive on the battery. Hook the black to the negative. We are going with Jim's labeling of polarity. If the charger is hooked up wrong the current limiting resistance of the bulb should prevent it from blowing out the charger. If the bulb glows measure the voltage polarity at the charger and determine if it is correct. It probably will only glow with the charger hooked up in one direction.
Good luck,
John