Would be interested to hear if anyone else has experienced this problem. If so might be good to take proactive measure.

 

I have and have had many cars 20+ years old and so far as I know, no alternators have gone bad. At least I haven't changed one in the last decade. That doesn't mean the brushes and regulators don't go bad though, I've just never had one seize as the OP's apparently has.

 

Well, the battery was replaced a few months ago. It was still the original. So I think the alternator was working super hard there towards the end of the battery life to keep it charged up. Probably wore the alternator down pretty bad. It was a damn hot day and I had AC and music cranked doing about 90 so I reckon it had just had enough. Definitely not something I'd do as preventative maintenance as the poster above suggested. Way too expensive a job to do "just in case."

 

I wouldn't be happy about an alternator failure either, but it certainly would not be reason enough to make me want to get rid of my Cayenne.
BTW, I have had AAA Plus for years as it includes flatbed towing free for the first 100 miles along with numerous other free benefits, like free gas, tire changes and locksmith services. I've used them all multiple times, and they have been quick to arrive, including flatbed towing twice.

 

I suppose that would make some sense with it being at fully duty cycle all the time.