That's true, but I'm not talking about disconnecting it and keeping it disconnected for an extended period of time. I'm talking about just as a quick test to se

That's true, but I'm not talking about disconnecting it and keeping it disconnected for an extended period of time. I'm talking about just as a quick test to see if the alternator is charging or not. Also keep in mind that all modern alternators have a built-in voltage regulator that provides first-order protection against such spikes. Empirically, I can say that I have done this very many times in my life, and I have never once observed any negative consequence as a result. YMMV, of course.