Can my car kill a battery in 2 weeks?

See post 4. Could not have said it better. Tenders are for keeping a battery topped off, not for getting it there, however, I still question the tender. Do you have a Volt ohm test meter? If not, get one. They're cheap. Disconnect the negative battery cable. With the meter set to measure DC AMPS, Put one probe on the end of the battery cable. Now strap the other probe around the negative battery post, leaving the meter between the negative battery cable and the negative post. Read the meter and see how many AMPS you have. I forget what's acceptable, but it AIN'T much. @67Dart273 (Del) has forgotten more about this kinda stuff than most these guys will ever know. I tagged him so maybe he will chime in and help.

No offense meant at all when I say this.....because lord knows I'm electrically stupid, but if you don't have SOME sense of electrical diagnosis, you need to be VERY careful, OR better yet, get a friend who knows some. These old gals are kinda picky in that area. The last thing you want to do is end up burning up a wiring harness.