reading this thread i'm really starting to wonder if i should really be buying a 35d....

I hear ya jhu321. I would have never thought I would be coming across this problem! Thank god for my SA and covering it under warranty as it should be! I have 16,200 miles on a 2008 X5 4.8i.

When I was having this issue with my E70 I had my battery changed too and the problem, which I experienced pretty often, never occured again.

I had the battery drain warning turn on today for the second time in a week. I have an appointment tomorrow but I'm worried that the dealer is going to blame my added sub for the battery drain. Has anyone else who installed an additional sub had this problem and what did the dealer do? Did they void the warranty if any on the battery?

High Battery Drain
 

It has nothing to do with the battery. Had the same problem last year and the dealer had the alternator changed. Discussed the situation with a friend who works for BMW in Munich and confirmed that some of the alternators on the X5 could be faulty and failed to charge the battery fully.
If you drive your car regularly your battery should not have the problem as the battery is designed for the full options on the X5.

Would the dealer give me trouble about my added sub. Would they blame it on the power usage from the stereo?

They probably will. I'd disconnect the amp's power, ground and remote wires and tell them you disconnected it all previously thinking it was the problem, but it wasn't. I'm saying this because it is a known problem that has shown to be common on this forum and I would try to avoid them being able to blow it off with the sub hooked up.

I'm not convinced of this any more I had the battery drains then got a 90aH battery replaced in it.. I had some malfunctions after a long drive 3 months back and nothing since and I only drive about 50k's a day .. 25k runs each...

It has been pretty cold over here in Belgium lately, and I rarely drive my car. If I drive it, only short distances are covered. Since this weather begun, I have the discharged battery almost every day. But I do not complain since the car starts every time. I only drive for a couple of miles so recharching the battery properly is out of the question.
Will hook it up today so it can be recharged.

Well, after our complete battery meltdown last year, when the low battery warning came on a coupla weeks ago I paniced.

Took the X5 to dealer, turned off engine, and it refired without problem. Naturally after a 35 minute drive, I figured.

The key readings showed no problems. SA asked if we left radar detector plugged in as "this is sometimes the problem." I suggested that since the 12V plugs were dead w/o key in ignition that it was not likely. :dunno:

Then he suggested a battery maintainer, and I said the dead 12V plugs made that difficult.

Night temps in 20sF lately, but car is garaged. No more problems. YET.