Im not sure how the alternator or AC Generator on the Boxster is much different than any other late model car. Before you do anything (except check for water under the seat on the ECU) with the car running get a VOM and check the voltage across the battery....if it is 13.8 to 14.4 volts or so your alternator is most likely working properly. This will only take a few minutes to do. If you do not have a VOM (Volt Ohm Meter) go buy one at Walmart, Lowes, Home depot or even Harbor Freight.....every car/home owner needs a VOM and know it's most basic functions.
https://www.youtube.com/watch?v=bF3OyQ3HwfU