Welcome Ben
You are not alone with this uses parasitic battery drain! Welcome aboard from my experience this is an ongoing issue with Lexus and to be honest the dealerships and Lexus customer care don't give a rats !Removed! about you and this issue's.
The remedy for the problem they told me to drive your car more often or purchase a battery maintenance charger and plug your car in, excuse me when you buy a vehicle you expect it to start every time you get into it and not have to worry if it will start.
I own a 2010 RX 350 with 50,000Km! and yes the car is parked in the garage for weeks on ends also my other vehicle which I have not experienced any issue with that one. My first Lexus and my last! this issue has been on going from day, one sorry to be a bearer of bad news.
PS if the Service department tells you did you leave your lights on or door ajar or anything to cause a battery drain JUST WALK AWAY.