[Gelbster]

Originally Posted by 10/10ths

....invest in one of these: OEM Porsche Charge-o-Mat Battery Tender Maintainer Trickle Charger 12V | eBay

Your car has several cut outs in the door gasket to allow the cable to pass through the closed door on its way to the cigarette lighter.

ALWAYS leave a parked Boxster on a trickle charger.
:

Be careful with Trickle Chargers. The cheaper,older ones are inferior to the new "Maintainers" like Ctek.There is lots in Search to explain why(overcharging).
.One of these connects to the cigarette lighter socket and is what the experts use:
https://www.amazon.com/CTEK-56-864-Automatic-Battery-Charger/dp/B006G14FK8
entertainment
https://www.youtube.com/watch?v=IdZES5CQz9I