We had our battery die two times in two weeks after I turned over my car to my wife. I never had a problem with it in the two years I drove it. We tried to figure out what she might be doing wrong to cause it. Dealer tested battery and charging system and said everything was OK. Here's what we think she was doing . . .
We think she was turning off the car while it was still in drive. If you turn off your car while it's still in drive, the ignition will stay on. You can get out and try to lock it (won't lock). Since the doors were all unlocked both times it died, this was consistent with the suspected cause. I don't know if this might be your issue or not. But, since pointing this out to her, it hasn't happened again and it's been several months.