No dimming of the lights. Voltages are good.
The alternator was replaced less than a year ago after a Subaru dealer supplied remanufactured alternator failed in less than 30k miles.
Battery, which also tests good based on the "cranking the engine without any problem" test, is less than a year old. It was replaced at the same time the alternator was replaced, likely done in by the alternator only charging it intermittently.
Battery and alternator cables are also good. I will probably check all grounds for corrosion and bolt tightness, although I don't believe the problem lies there.