scimitar1,
Lead acid chargers are almost always constant-voltage chargers, and when you plug them in you will find that they put out a steady voltage a little higher than the batteries to be charged.

If you'll just disconnect the charger from the batteries, then plug it in, (assuming that this is not some really complicated, computer controlled charger) you'll find that it puts out somewhere between 14 and 18vdc unloaded. Just read the polarity with your meter, then connect + of the battery to + of the charger, and - to -.

Joe myers