Something is wrong here, if your alternator is putting out 13.9vDC at idle, after a long drive the battery should be charged enough to not be dead, dead, dead 15 minutes after returning.

I would try getting it started up again and rechecking the output, see what you are getting at idle and then watch the meter and see what happens as you raise the RPMs, to maybe 2K. Output should remain basically static, it might go up a very little but should hold about the same. Another way a regulator can go bad is by overcharging. Let us know if the output increases and what it increases to as the revs come up

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.