Our 2006 Z4 BMW (14,500 miles) has been to the dealer three times in the past 6 months because the car would not start - dead battery.
* The first two times we did not even get a click out of the battery; the third time it at least clicked.
* The first two times the car sat for 5 days without being driven; the third time it was driven the night before.
* It is kept in a garage so we could see if there were any lights left on-and there were none.

The dealer claims that we must drive the car at least 20 miles a day to keep the battery fresh. We drive 28 miles 5 days a week and the car is used 7 days a week. The dealer supposedly put a new battery in the first two times, courtesy of the dealer, and now says that we need to hook a trickle charger up to the car every night if we want to be sure the car will start. They also claim that the batteries were not defective, but not charged - but replaced them as a curtosety.:banghead:

When the dealer calculates a daily miles driven, they calculate 3 months at a time and we fall a few miles short of their 20 miles per day. I have requested something from BMW corp regarding the 20 miiles a day but don't expect anything.

Kodos to BMWUSA! They sent me an e-mail within a few hours. To paraphrase the email: they are aware of the problem that I am having and agree with the dealer that we simply are not driving the car enough to replace all of the energy that is used by the high tech insrtruments on our short trips. They further agreed that we should purchase and use a trickle charger on the car to insure a fresh battery.
Any suggesting/comments?:2cents:

just fyi, I have a 2005 BMW Z4 and it sits from Nov to March during the cold months (Northeast). I start the car once yes once a month for 15 mins and that's it. It sounds like you have a electrical draw somewhere in the car. Anything attached in the lighter socket that may be on when you park the car? If not find someone that knows electrical work to check the car out. Batterys don't go dead by themselves.

during the summer months I drive some times 10 miles a day and only a few days a week and still never had a problem. BMW needs to look at the car and determine whats wrong. No guess work....OH by the way my car is fully loaded auto roof etc. one other note if a power top make sure when you put the top up or down you have the motor running..