I'm also having problems with dying batteries in my '16 Legacy. I replaced my OEM battery with an Odyssey Extreme Group 25 that lasted a little over 2 years. I put a voltage data logger on the battery, and found that there is a seemingly random, periodic parasitic draw when the car is off that lasts anywhere from 30 minutes to 3 hours and drops the battery voltage about 0.1V for each occurrence, 2-3 times per night. After 2 days, the battery charge is pretty low. Compounding that issue, I found that when the car is running, the alternator is off about 1/3 of the time, and the battery drops down to ~12.2V. The battery usually comes back from short trips at a lower state of charge than when I left. I fully charge the battery every week or two with a Victron charger, but that's apparently not enough.
