Can my car kill a battery in 2 weeks?

Two weeks ago, my 64 Sport Fury would not start, so I attached the Battery Tender and tried to charge it. The Tender light just kept blinking yellow (meaning the charger is working properly) after many hours. I took the DieHard to Advance Auto Parts since they handle DieHards now that Sears is gone. They tested the battery, which was only 1.5 years old, and said it was bad. They gave me a new battery (under warranty) at no charge. I hook up the new battery and the car starts right up.

Yesterday, I go to start it – and nothing. I put the Battery Tender on overnight, and today the yellow light was still blinking. It had not charged at all. No dim lights, or anything. I did not test the voltage. There is no history of battery drainage on this car.

Is this another bad battery, or is my car a battery killer? I’ll take it back for testing, but do you guys have any thoughts on this?