My test was the car struggling to start. I didn't need a tester to tell me that. It took so long because I went to the dealer 3 weeks ago, then returned two weeks after that. You know, life. In the meantime, I bought that tester to prove my point. Ironically, the tech never even asked to see it.

Yes I understand that life part, but. Did you buy the batt from parts and install yourself? Or did you pay to have the dealer install it?

Many months later I want to put a final followup to this thread.
The problems with battery drain and iffy starting continued to haunt me long after I stopped following this thread. I'd charge the battery to drive 3 miles and then have to jump it to get to the next stop and then jump it again to get home. Earlier I had taken it to the dealer and they could find nothing wrong with the car, but explained that the way AGM batteries cycle through discharge and re-charge made them a bad fit for my car. In January I had installed a new Optima AGM battery because I had such good experience with them in my older cars, 1920s-1980s. It was with this new and pricey Optima that I was having the problems, but I didn't believe the dealer techs because of my prior good experience with Optimas. They blamed the battery, it even failed one of the tests they ran. The battery, however, tested fine at the shop where I had purchased it.
With winter coming I decided to take a chance and replace the battery again. That was November 4th and the car has been positively trouble free since then. In those first weeks I was regularly surprised at the features that started working as they should. On 5 degree mornings after a day of limited stop and go driving the car starts more eagerly than I had ever known. This battery was half the price of the Optima and would have been even cheaper had I thought to get it at Costco. I've read on this forum that these cars go through batteries regulalry, but when the time comes to replace it again I'll go the same route.
I do regret doubting my own instincts when I followed the recommendation to replace the Network Gateway gizmo. Anybody want a new one? My car's VIN said it was unlikely to be the problem, but I went with it anyway looking for a miracle when I just should have believed the dealer.
Months later the car is just about as dependable as the '92 Buick that was replaced with the Lexus.