Electrical / Battery issues

[ozam]

I have a 2007 X5 4.8 CPO that I bought back in 2008. Starting about six months ago the vehicle started experiencing strange electrical problems. As the X5's voltage starts dropping all types of error messages (transmission, 4x4, etc) start popping up and the car eventually locks itself down leaving my wife stranded on the side of the road. The telltale sign of an event about to happen is the when comfort access stops working and the clock resets itself. Strangely, the car has never had an issue starting and the problem seems to get worse while driving. The car has now been in the shop at least five times for the same issue.

The dealership has come up with the following issues (in order that they were given):

1. vehicle checked and nothing wrong
2. bad battery connection
3. replaced drivers side door handle (excessive electrical draw)
4. the car is not driven far enough on each trip (this despite the fact that it gets 15k per year and my wife's driving habits haven't changed since 2008.

The dealership now says that I need to buy a trickle charger and recharge the battery periodically (and who knew the X5 was a plug-in hybrid!!??). While I understand this "solution" it just does not make sense in my situation because the first time this problem arose was the day after a 400 mile drive!

Ironically, on Monday on the way to the dealership to get an oil change all the warning lights etc came on just before she got there. They charged the car for 1.5 hours and sure enough the next day an "excessive battery discharge" warning light came on. The car is as that the dealership now.

So the question is how do I handle the dealership? I've read other posts written by people with similar problems but I have yet to see a resolution. While I've been as nice as possible with the dealership thus far, it is absurd that I keep having to drive a car that has more than a remote possibility of breaking down. Thoughts?