+1 for the CTEK unit. I've been using it on my GT4 during the wintertime. What convinced me? Finding the Porsche's battery dead after a few weeks of sitting. Where's the battery? In the front trunk. How do you open the front trunk to access the battery to recharge it? An ELECTRIC switch next to the driver's seat. A switch that won't open the front trunk when the battery is dead. Turns out I had to connect an external power source to a special metal connector in the fuse box to be able to open the front trunk with a dead battery. Then I had to jump start the car with jumper cables, because the roadside assistance guy's battery charger didn't have the required juice to restore the Porsche battery. The official "Porsche Roadside Assistance" guy turned out to be a local third-party guy who had never dealt with this type of situation before. I googled it and we figured it out together. Nice enough guy, but he had no clue. Not very reassuring, Porsche.
So get a quality battery maintainer like the CTEK. Well worth the money!
