This is the US version of the battery maintainer I bought:
http://www.ctek.com/US/MUS3300/features_benefits.asp. I believe they make the one that Porsche sells and re-badges. Check out the videos and the higher end models.
I bought the CTEK cigarette adapter for the unit, and the 7-pin to 12V adapter (for the trailer hitch). I back it in towards the garage door (as it won't fit in there), and plug it in after every drive (like a big expensive iPod). I also have the eyelet connector attached to the battery in the event I pull in nose first.