Can my car kill a battery in 2 weeks?

Battery tenders are notoriously slow charging at very low rates. They are tenders not chargers. You might want to check yours for output. Some of them will not charge at all if it senses a very low voltage. If the drain is greater than the Tender output, it simply cannot keep up.

But you should know that your alternator output stud is always connected to the battery, there is no way of shutting it off. Inside the alternator are 6 diodes, all connected between the battery and the ground which is fine until one of them decides to leak power. When this happens, it will run your battery down.
If just one is leaking you may not notice it on your ammeter, and the car will otherwise operate normally, allbeit with a slower and reduced rate of charge. You can test for this with your A/C voltmeter, on the output stud with the engine idling; it should not be there.

30/40 years ago Sears DieHards were a pretty good Battery. I cannot say if that remains true today.