2018 Legacy Dead battery every 2 days for 2 weeks now. Dealership would not replace it today because it registers as a good battery.
Well that battery is not going to last long being drained that often. It would help the excellent mechanics on this site if you gave more information. Such as what did the dealer say other then the battery test good ? Have you added any aftermarket items that might draw current ? Have you had the alternator tested which your local Auto Zone might do for free ?
Dealership should have checked the alternator since it’s still in warranty. Are you taking very short trips while still dark out? In addition, do you sit in the car with radio on and/or other accessories while the eng is off.
When did this start happening, gradual or all of a sudden?
Is there a light on in the trunk? Are the dome lights left on? When a good battery dies quickly something is on when it should not be on. Some times easy to find sometimes PITA
You most likely have an excessive current drain on the battery while the car is parked. Something is drawing power from the battery when it shouldn’t be. Have a shop check for a parasitic current drain on the battery. Normal current draw should be less than 25 milliamps while the car is parked and things have gone into the sleep mode.