Last night, I left my phone at car, and nothing happened.. I was able to start the car no problem and shows bluetooth connection right away..

If in fact, your phone made drain your car battery even you turned off the engine, this should be very annoying that you have to turn your phone off everynight..
What if we have to use phone for oncall 24/7 purposes????

I have to turn my phone 24/7 due to oncall issues at night. at your case, I can not leave my phone on at night due to battery drain of bmw? this seems to be not right. I can even get BT connected from my bedroom.. and I am sure, it will drain out the battery which in your case..???

 

I would try a different Bluetooth mobile phone and leave it on and see what happens. Could just be a weird match between the car and that T610.

 

It took 3 weeks from a brand new battery for this to start happening nightly. I believe it is a very low draw on the battery that takes time to get it to the point where it can happen overnight.

I verified this behavior again accidently yesterday. Thought I had turned the phone off in the monrning when I parked it at work. Tried to start the car in the evening and wouldn't due to low battery. Checked the phone and found it was still on because of the keylock. Left the car overnight and took the phone with me. This AM it started up just fine.

So, whatever is going on is definitely related to the phone. It is a T610 with early firmware, so it may be a problem specific to that phone. And it takes awhile to drain the battery low enough for it to happen overnight.

 

It took 3 weeks from a brand new battery for this to start happening nightly. I believe it is a very low draw on the battery that takes time to get it to the point where it can happen overnight.

I verified this behavior again accidently yesterday. Thought I had turned the phone off in the monrning when I parked it at work. Tried to start the car in the evening and wouldn't due to low battery. Checked the phone and found it was still on because of the keylock. Left the car overnight and took the phone with me. This AM it started up just fine.

So, whatever is going on is definitely related to the phone. It is a T610 with early firmware, so it may be a problem specific to that phone. And it takes awhile to drain the battery low enough for it to happen overnight.
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Very interesting to know. You might need to change your phone..Since Mine didn't happened when I tried and I am using Cingular Razr V3..