I take it no one has invested $150 in the purchase of an Optima battery?

Optima 12 Volt Performance Battery - Sealed Batteries by Optima

I doubt the X5 is anyone's first vehicle. We all know BMW is going to drag their feet on this issue.

Lots of vehicles have suffered from such issues. I remember my 1997 Jeep Wranger has a similar issue and went through multiple batteries (I owned two 1997 Wranglers a 4-cyl and a 6-cyl.).

If this happens to me, I'll just replace it with a "Yellow Top." It exceeds BMW's specs., hence there would be no warranty issue.

I agree with all: an X5 that discharges its battery after sitting for several days is suffering from an error.

It's entirely possible that BMW purchased a massive batch of bad batteries. Batteries are all rated, and there are tremendous variables between batteries. In fact, when it comes to high performance batteries, they're rated in terms of the time they take to discharge when a certain load is placed upon them.

There can be variances of 20% to 30%.

Battery tender requirements are fine, but having to do so, in a tepid climate is ridiculous.

Is anyone in California (Southern California), or Arizona having this issue?

I'm going away Thursday-Monday and my X5 35d will not be started. We'll see what happens.

BMW will certainly be getting an earful if my 35d doesn't start, and this thread is excellent evidence for all of us, so keep it going.