If I use my 3.0d as you describe (short runs, many starts per day) I don't get a week out of it before the battery begins to show signs of depletion. It just isn't being run enough to restore the charge lost from starting...

First indication of battery depletion is the DSC lamp flashes up as I crank the car. I notice this because I always wait for the ABS and DSC lamps to cycle off before cranking. If the DSC flashes back up on cranking, the battery is getting critically low.

I overnight charge it that night, with my trailer connector charge cable. Job done.

__________________
Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)