Does anyone have any information on installing the supplementary trunk-mounted battery in a 2004 Cayenne that didn't come with it? I am thinking about upgrading the stereo (amps, etc.) and I am worried about the drain on the single battery with all the electronics already in the car. My dealer says I have good reason to worry. It seems to be an option these days; but it wasn’t when I ordered my car. Is the wiring harness for the second battery in place?
The tech bulletins say that the second battery is only used to start the engine when the standard key is used (not used with entry & go