I really enjoyed this article and linked items. I remember way back when (more than 3 decades ago) I would manually check the waveform coming form the UPS, doing battery checks (really cool batteries in transparent cases) for level, crud accumulation at the bottom of the batteries, specific gravity, and connection checks. There were certain cables that I'd grab with my hand to check for warmth and do crazy things like walk around the back of machines to feel if the fans were working "at speed" and around the front to check "activity lights" (disk, cpu, etc) and check routers for "collision lights".
I'm REALLY, REALLY glad I haven't had to do that type of thing for the last 3 decades. 😀 And, it's gotten even better... I don't even have access to the "Server Room" anymore. 😀