These cars don't seem to respond well to anything other than normal operating parameters. I had mine in the garage for quite a long time, couple of years actually. I had a battery maintainer on it the entire time to avoid any issues. Still, when I put it back in service, the nav computer was dead, no video signal. I felt lucky that was the only thing as replacing it was literally a five minute fix :-)

A battery maintainer is definitely the better way. CTEK seems to be a decent brand (Porsche recommends it for their vehicles).

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2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.