Battery Isolator and Misc Charging ?

[Hotrod]

Hey yall needing some opinions, thoughts, and suggestions for my voltage setup.

Well my alternator went out sometime between sunday-monday (not sure why) and I am having major voltage drop. I have a stock 90a alt and three batteries. (Optima Blue Top, and 2 Sprinter 106lbs). They are all hooked up with 1/0 wiring from KnuKoncepts. I also have the Big 3 done with 1/0ga KnuKnocepts.

1. I was wondering why all of a sudden my alt died.
2. Should I get a Battery Isolator so I can charge each battery one by one (told it would be smart to)
3. What size Isolator?
4. Would a Duralast Alternator (autozone-$140) last me for a little while until I get a big boy one (after asylum).

HELP! my stinger voltmeter says i am at 12-12.3. I am gonna charge my batteries all night to try to get a new one tomorrow. but need your thoughts on it all.

[Hotrod]

Could the Serpentine Belt be the problem?

[UV7]

First and foremost, I recommend that you take the alternator out of the car and go have it fully tested several times. This will give you an idea of where to go from here.
More than likely, if you're experiencing voltage stability issues, then your voltage regulator on the alternator may be dying. This can happen, especially if you are banging the daylights out of the charging system with LOTS of current draw. Keep in mind, if the voltage regulator is flaking out now, it isn't going to last very long before it completely dies on you. Don't try to push it and make it last for a few days. More than likely, it will give out the first time you're out for a decent drive and will leave you stranded.
As for the battery isolator, this isn't going to solve your problem. A battery isolator does not typically allow you to charge one battery at a time. In fact, it works quite the opposite. A battery isolator disconnects the secondary battery(ies) from the main battery that powers the rest of the vehicle when the ignition is off. This prevents the audio system (wired to the secondary battery(ies)) from draining the main battery, preventing it from starting the car. When the car is started, the battery isolator connects the main and secondary batteries together, allowing the alternator to charge everything. Unless you're banging the stereo for long periods of time with the ignition off, I don't recommend running a battery isolator. It would be a waste of money and would only introduce resistance into the charging system resulting in a drop in voltage.
If your voltage regulator on the alternator is dying, then you have no choice but to replace the alternator. If you're in a monetary bind and can't afford a HO alternator at this time, then swapping in another stocker will work for a while. Just keep in mind that banging away at the charging system is going to eventually yield the same results, so you really should aim at getting yourself a HO setup. It will not only be better for your sanity, but will overall be better for the car and your audio system.

[how much air]

Might only be a faulty voltage regulator or the brushes may worn out....if that's the case, no need to buy a new alternator, just replace the faulty component. Find an auto-electrical shop that rebuilds alternator and starters....every town has one....they can help you out.