Thanks for your reply, Shadowfax. I’m feeling a little silly that I wasn’t even generally aware that an owner’s manual suggests replacing certain parts on a basic schedule. I’ll check that today.
Yes, it took Advance several consecutive tests before the read-out said the three-week battery was not simply uncharged, but needed replacement. I also didn’t mention another alternator test (in between the two I listed) with the current battery, in which Advance’s computer said the alternator was officially “good” but still generated excessive ripple. So I share your lack of confidence in their assessment.
I plan to get the compressor belt tightened a.s.a.p.