Multiple alternator failures on 2001 Subaru Outback

I have a 2001 Subaru outback stationwagon (2.5i engine) with 85,000 miles. I live in Los Angeles so the car is never in freezing conditions and it rarely sees rain. About 1 year ago I replaced the battery after it would not old a charge. This did not fix the problem and I brought it to an independent shop where they replaced the alternator. A few weeks later the car started running rough, with warning lights, and gages not working. It eventually stopped running completely and was brought back to the same shop where the alternator was replaced again.

After this time if the car was not started for 2-3 days the battery would be dead, but once jumped the car would run fine for an indefinite period. I suspected a problem with the new battery which was only a few months old and brought it back to Sears. They checked it and could find no problems and refused to replace it under warranty. This problem continued to occur and I brought it back to the shop that replaced the alternator twice. They said the car had no problems and it was 'normal for the battery to die unless the car is run everyday.' I took it to a second shop to check, they said the alternator was fine and it was a battery problem. They also confirmed that their was no drain on the battery. The problem continued to occur so I bought a second new battery and installed it (Sears would not replace it under waranty as they could not find any problem with the battery).

The problem improved with a new battery but the car would still occasionally not start if left for a few days. Meanwhile the old battery sits in the back of the car and holds a charge for several weeks until it is needed to jump start the installed battery.

Next the battery and brake light would come on occasionally for about 20 minutes then go off. I checked the current entering the battery when the car was idleing at it was 130 amps, which seemed a bit high to me. The voltage with the engine running was a bit over 13 V which confirmed that the alternator was working.

I brought it to an independent shop and they could find no problems (I was never able to get it there when the warning light was on). This weekend after driving the car for about 100 miles multiple warning lights came on (alternator, brake, abs) and the gages stopped working. I barely got the car to the Subaru dealer in Bakersfield. They confirmed that the battery was dead and the alternator was not producing enough current under load. The alternator was replaced a 3rd time. The also checked and confirmed their were no drains on the battery or unusually loads on the alternator.

Either I am really unlucky or there is some underlying undiagnosed problem here. Any idea what it might be?