Porsche Repair Questions? Ask a Mechanic for Answers ASAP
Hey there, thanks for the question.
I assume you checked the charge rate under a full load? If so at 2000 rpms you should expect to see from 14--14.5v. At idle your readings should be close to the same.
If there was an issue with overcharging causing battery leakage or high readings at 2000rpms then I would say for certain it's the voltage regulator. At this point though just from a low voltage reading it could be the regulator or the alternator itself (brushes, bearings, etc). While the 996 engine isn't the most difficult to replace an alternator on, you can bet it will take you around 4 hours if you haven't done one before. Depending on valuable your time is to you, a rebuilt alternator or having yours rebuilt while out is probably the best bet.
If you have more questions though please let me know i will be happy to assist further.
If not just be sure to leave a kind rating when were done is all.