99 cl500 starter/battery warm start problem

Hello,
I should start by saying I’m in love with Ruby! The ride, the power, the grace of this car is amazing.

I’ve spent some serious money at the MB dealer, rear struts, actuators, brakes, rotors, tires, starter, battery, oil pressure sending unit, central locking pump, and last but not least a complete service.

So here is the problem. When she’s cold the engine turns over fast and starts immediately. On short trips she starts right up, no change.
On a longer trip, the car running perfectly, oil pressure and engine temp normal, the battery seems dead when engaging the starter. The engine will barely turn over, service and warning lights go dim, try again and you even hear the tick of what sounds like a completely dead battery.
The first time this happened the dealer said it was the starter and I had it replaced. At the same time we replaced the battery with an almost new one.
I had no problems for a month or so (keep in mind my trips were short around town). Yesterday I drove the car 100 miles, AC on everything working perfect. Turned her off, turned the key on and the engine barely turned over, tried again, completely dead.
I went to my appointment and returned an hour later. The engine turned over very slow but started.
Drove home, again, 100 miles no problems, half the trip at night.

The next morning the car turned over like a highly charged battery. After a 30 minute trip with two very slow starts in between the battery went completely dead again. AAA used a battery pack to jump the car.

I had the MB dealer bring a new battery out. First he tested the battery and said it was good, and then a re-test showed bad. He went ahead and put the new battery in and the engine turned over fast and started. He let the car idle for about 20 minutes, turned it off, same thing, engine wouldn’t turn over.

What should I be looking at?