Here is what I've figured out from this thread and other sources.
I verified I was already doing it correctly.
My Buick has Vasoline on electrical contacts. My Jeep XJ has CRT brand pink terminal protector spray on electrical contacts. In both cases applied to contacts before bolting together and again after bolting together.
CRT terminal protector spray is same type stuff as Permatex terminal protector spray. Same stuff, different brand.
Both of those ^ are acceptable methods. The potential downside of vasoline is dust/dirt will stick to it. Over time it can get dirty. The spray protector is better IMO because dirt won't stick to it.
I'm sure all the other methods/substances people recommended are also fine, except dielectric grease.
Dielectric grease is an insulator,
NOT a conductor. My common sense tells me NOT to put dielectric on battery terminal contacts. Am I misunderstanding something?