Alternator failed and came back to life?

Anyone had this experience before? I'm a noob here on electrical and alternators.

I was driving and made a pit stop. Turned off the car went to restroom, turned it back on a minute later to head home and a screeching rubbing sound came from the engine area, with the red battery light on the dash. I opened the hood, saw nothing immediately wrong. Belt was intact and spinning, fan was spinning. Turned off car and turned it back on, same thing. Voltage reading from my cig. lighter reader says 13.3 (but it always reads low vs the battery by .3-.5, so probably something like 13.6-13.8?).

I figure if the alternator is out, i can still make it 15 miles home so im not stuck, so i just start driving. To note, as i put it in reverse, the screeching lightens up significantly.

Driving 60 on Hwy, the voltage remains steady reading 13.3 (13.6). Half way, i remember that i've got my headlights on and it isnt quite sunset, so i turn them off. Voltage goes up by .1. A minute later the red battery warning symbol turns off, and the voltage slowly increases up to 13.8 (around 14+) over the next 10 minutes.

Tested this morning, and got 12.6 at the battery, car off. 14.0 with car on. and dropped below 14 successively with lights on, radio on, phone charging.. down to 13.8.

Does anyone have insight into this? I've been told alternators go out and dont come back - so this seems unusual. I already ordered a new one, but the current original one seems ok? I think i'm still going to replace it? or is there anything else I can/should check?

SWhat is the cause of the screech noise? Was it the belt rubbing on alternator and would that damage the belt?

2011 v6 4x4 with 140k Miles.

 

Had a similar situation on my 96 4runner last month - was on a 300 mile road trip, everything was fine. Stopped for gas, got back in and a couple miles later the battery light came on. Voltage reading on my Scangauge was around 11.5v give or take. Was still running OK so I decided to just keep going. About 20 miles later it suddenly jumps back up to 13.5-14v and the light went away. Then some miles later came back.

Went like this back/forth for a bit until eventually it just stayed on, luckily I made it to my destination with it operating at about 11v. From what I've gathered, if a key component like the bearings fail then the alternator will fail full-stop. If it's the brushes going bad, it can go in and out like that. Run weak for awhile before failing completely.

I replaced it with a new Denso unit and it's been running right ever since. Original had 272k on it when it went, so it definitely served it's time

 

Alternators can actually drop in and out.. the screech sounds like it may have been seizing up though. You can wait till the problem comes back .. or do a little digging and take the belt off and check all the pulleys for anything rough or scratchy. If the other pulleys are ok I'd personally think about replacing the alt before it fails again

 

It could be the A/C Compressor or clutch....

 

Definitely sounds like the alternator is failing I would replace it. My moms jeep’s alternator started smoking once and it has been years since that happened and it has been fine.