Sorry for the delay and thanks to everybody who shared their expertise. I talked to my local mechanic and he said without hesitation he agreed with the remote mechanic’s diagnosis (bad reman alternator right out of the box). I had the remote mechanic proceed with installing a new alternator. After that, it worked fine. Consistent, sustained 14.2 V across the battery terminals. Picked it up last week and drove it 5 hours home no problem.
The mechanic in Springfield, Va was great. I’m new to this forum so I don’t want to break any rules by endorsing a particular business, but if you want the name, PM me.