Another Dead Battery Thread

[socalsharky]

I realize that there are numerous dead battery threads here, but my situation is slightly different.

I only drive my 07 Boxster S on the weekends, and sometimes not for 2-3 weeks at a time. I know that is hard on the battery. So when I couldn't get it to turn over a week or so ago (I did get a solenoid clicking and the instrument lights worked), I figured that the OEM battery was shot. Got the correct Interstate replacement battery, installed it and everything worked great, or so I thought. The car started right up, and I drove it about 60 miles that day without a hitch. The following weekend, I went to start the car and it was dead as a hammer. No solenoid click, no radio, no instrument lights, nothing. I couldn't even extract the key from the ignition.

I got jumper cables to open the hood, and a battery charger to recharge the battery. The battery took about 12 hours to charge on the 6 amp setting, which seems about right. When I connect the battery the alarm goes off and everything seems to work, but I still am concerned.

What could have made the replacement battery go COMPLETELY dead so quickly? I am afraid something is putting a big drain on the battery while it is parked, even though I lock it to shut everything down. Could the battery be defective? If it was the alternator, wouldn't I get an indication on the dash? Any thoughts or previous experiences would be appreciated.