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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). I would think that this would be an idea stable power source for a high end stereo.

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As I said in the other board post, you basically can't do it. I looked into it. It's not just the battery and cabling, but a whole series of electronics like isolators and controllers that have to be changed out. It's also a software problem.

Turns out it won't help your needs a heck of a lot anyway. Like me, you have too many power-hungry toys. What I did was to physically install a solar panel trickle charger. You can buy the ones you throw on the dash that plug into a lighter (best are 1.8 watts), or you could hard-wire a panel as I did (5W). I will post pix later today.

If you are near an outlet and expect to leave your rig for some time, of course you can always plug in an electric trickler.

I have a pic of the solar panel here....Pix page

http://www.villagephotos.com/pubbrowse.asp?selected=748418

Edited by jdrive
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A little more info....

The MY03 Cayenne's (until April 28th, 2003) all had Auxilary Batteries and TSB 1/03 2706 describes how to install it. After that Porsche moved the Auxilary Battery to an option status (Option J2C) for MY04 cars (TSB 2/03 2706). So the good news/bad news is that if you have a MY03 you likely got the 2nd battery included and the MY04's will only have it (and the wiring harness) if it was ordered as an option.

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