Update on my high battery drain: I drove my 535 four times in 2 weeks, did not use the battery tender in these 2 weeks. I never had the high battery drain fault.
Yesterday, I decided to hook up the battery tender so I popped the hood and connected the battery tender up the positive and negative points under the hood. The next day as soon as I started the car, I had the high battery drain fault.
Would it have something to do with the hood open overnight?

 

I'm no battery tender expert -- is the tender supposed to be connected to the terminals under the hood or directly to the battery? Maybe the tender itself prevented the car from entering sleep mode?

It sounds like you don't need the tender anyway...

 

When you leave the hood open, it prevents the car from going to sleep mode. I use a tape over the hood switch and it allows the car to go to sleep mode.

 

Thanks for the tip. I'll give it a try.

 

My car is more of a garage queen. I won't use it in the rain or snow. So I'd like to keep the battery tender on it because I know I'll eventually kill the battery.

 

This is really interesting -- I didn't realize that the hood being open prevents the car from sleeping. This would certainly explain the high battery drain error coming on whenever I use the battery tender. I suppose another way of dealing with this problem is to close the hood lightly over the wires.

 

The tender is supposed to be connected to the terminals under the hood. For some reason, the battery won't charge properly if the tender is connected directly to it (this is according to my S.A.)

 

My float charger is hard wired, directly, to the battery term (+) in the trunk. I can't vouch for others but my setup does charge.

Ask the S.A. what "charge properly" means. I think he is stretching your chain.

sixcard

 

and with hood open charging via the terminals there. It wakes up as soon as the hood is closed which I avoid doing until I use the car right away (OK it's in a locked garage).

 

I've been using a Deltran Battery Tender Plus on my '08 535i for about a year now. I have the Deltran cable connected to the (+) and (-) terminal points under the hood and the other end is the tender connector. So I have it connected with the hood closed. I have had no problems at all.