You abused the battery so it probably died. If that was all that happened, it is an easy fix and no need for a special Porsche battery, any of the correct size will do. And if you get the battery into any place that sells batteries, they will run a test for you in a twinkle that confirms they need to sell you a new battery. You can take the battery out and install the new one yourself without any risk of stalling and not having juice to start by just removing two access screws, lifting the cover and climbing in the front trunk and removing the battery....with the key out of the car and the radio code in your pocket if the radio needs one.
It is out-of-hibernation season, batteries are failing left and right.
A list of batteries that are known to work at
here