Excessive Alternator mechanical load and belt squeal

A friend of mine always had trouble starting this car so he gave it to me.

Hard to start from excessive mechanical load for the alternator belt, due to failed alternator bearings. I charged the battery and removed the belt, and it was really easy to start it from then on.

I replaced the alternator with an AutoZone remanufacture, and then got busy with other things and went 2 years with the new alternator installed but not tested.

When I got around to starting it with the new alternator, the belt squealed every time, and pretty much all the time. After re-adjusting the new belt tension several times, with no reduction in squeal, I determined to replace the alternator again, this time with a Real OEM unit. Got a good deal on one from a Mazda Dealer, a remanufacture with the right part number.

The improvement was great.

However, it still likes to squeal a little sometimes. But turn off the lights for a moment, and then you are usually good to go.

I read in several places about this tendency with these cars.

I want to pay the price to finally get this thing fixed right, and but good.

The question is, can this be caused by excessive resistance going to the battery? What about the voltage regulator being too enthused? Should I just let an auto electric shop assess and fix it? Is the problem likely outside the alternator unit since two new remanufactured in a row loaded the belt too much?

Why is this problem not more commonly discussed, or ubiquitous?