When I changed my battery in December voltage was 13.5 while running.
I mean short of running Test 9 all the time - no way to really "predict" IMO - I have had zero symptoms - maybe twice in the past 4 years I had a random xenon flicker (turned on and off randomly a few times then stayed on and threw a low beam error) but it was totally random and nothing else.
Like I said I had about 8 miles of driving with the battery light slowly flashing on and then off again - then it stayed on as I was getting to the gas station and when I restarted after I filled up (with the AC off now) - I was at 11.1v so I knew I was fucked.
I guess if you see the temp extremes we can get in Jersey (up to 110 ambient in the summer, below 0 in winter) I would say those alternators might be the hardest worked - if your climate sees less extremes then maybe even if your X is older than mine (mD for example) you may get more life.
This has nothing to do with mileage by the way and everything to do with temp extremes and age - I have 88k miles. And I probably have more electrical load with my xenons, 2-axle air suspension, etc.
I will say it is one of those things I would replace preventatively "while I'm in there" or if I had to take the belts off, etc.
On the 3.0 if one was having the OFHG leak for example I would replace the alternator since you have to remove it anyway - I don't have the leak so I didn't get the opportunity. Also I guess if you are doing belts, tensioners, etc it's kinda right there so would be good to get tested.
Anyways I'll update as I get my X back - would be nice if I didn't fry my new battery as well.
Oh, and g300d - thanks for the wishes, although I'm a few weeks shy of my 30th birthday - picked myself out a Walther PPQ M2 9mm - I'll post updates in the "other thread"
