Thought there was a post a few weeks ago in the 6.0 or 6.4 section about the alternator getting flaky, with a cracked or broken bridge in the back of the alternator. I would be inclined to remove the alternator and look it over real good, and have it load-tested if you can. just a thought. I replaced my alternator in my 2000 4 years ago in January. It checked out ok on the load tester, but, I was in zero degree weather, with a set of 3 year old Duralast batteries that were questionable (found this out when the truck wouldn't start in zero degree temps). Since I was 750 miles from home, I went ahead and put in 2 new batteries and a new alternator, and all has been fine since. Also, check the battery cables really good. I had a set of cables on a Nissan truck that looked ok at the terminal. The charge light kept coming on, so I replaced the alternator, only to find out (after the fact) that the cables were half-eaten up inside the wrapping. After that experience, I always check the cables as far as I can get the wire exposed to see if there is any rot/calcification going on.
just my .02 cents worth
Y2K F250 CC PSD Auto, Short-bed Lariat, Woodland Green/Gold, ordered 07/10/99, born 09/12/99, delivered 10/08/99, Access bed cover, Bed Rug, Zoodad mod, Viper Remote Start Alarm, Fumoto valve, 125K somewhat error-free miles (so far) [never back to dealer for anything]
Repairs: CPS, Water Separator Valve assembly, rear axle bearings, VSS, batteries, brakes, alternator, serpentine belt (x2), driver door pwrlock actuator, water pump
2009 VW Tiguan 2.0 l turbo 200 hp gas engine (TDI engine not available for it yet)