So after tracking down and fixing boost leak number 463, my car decided it wanted to take up more of my long weekend and threw the battery and brake lights upon starting.

Voltmeter showed a steady 12v when running, so that's a pretty good indication that the alternator has finally gone (never replaced it before)

I took the opportunity to buy a reman'ed one from AutoZone and spent my afternoon putting it in -not too hard.

Upon firing up the car, all seemed well -the lights on the dash went out, and my voltmeter was showing the healthy 14v.
I let the car idle for a bit, rechecked the belt tension, and went for a drive to return the core.
Half way there, the volts dropped to 12 and stayed there.
At the autozone, we checked the battery, and it was showing ~10.8 v when running, and it seemed like the new alternator had quit.
The thing is, there are no lights on the dash to show that the alternator is dead, or that the charging system is off.

So now I have 12V of power, but no dash warning lights. If it wasn't for my volt gauge, I wouldn't really know if something was wrong until I finally ran out of battery power.

Now, I know these reman'ed units are usually crap, but come on......15 min and it's toast?
I know everything is hooked up right, because it worked when I started it.

Thoughts?

Have your battery load tested. I've done more than a few alternators because of a bad battery (and visa versa). A battery that has an internal short can cause all kinds of wierd things to happen.

Definately get the battery tested-they can do all sorts of dumb stuff with just one bad cell, or just get a new one if you are $$ and lazy. There is also the voltage regulator to worry about, not sure what they consist of on our cars (knock on wood, haven't gone there yet)

The voltage regulator is built into the alternator.

Got the alt replaced yesterday with a genuine Mitsubishi rebuilt unit. (hurray! another rebuilt item at more than double the price of the crappy Duralast one!.....whatever)

My battery voltage never dropped below 12v during the time I got from my house to the dealership.
I have been told that if you do the alternator, you should replace the battery as well, but then when I say I have one of them there funky Optima Red Top batteries, then the response is always: "oh.....in that case, never mind.......those red tops are awesome blah blah blah"

The deep cycle nature of the optimas mean they can be 'discharged" to 10.5 v without any problem.

Anyway, everything seems to be working fine now, volts are between 13.5 and 14 under normal operation.

Should I replace the battery anyway?
DSMs are kind of finicky that way in regards to the relation between the battery and the alternator, but at $150 a piece, these batteries aren't cheap, so I don't wanna hafta buy another one of I don't hafta, youknowhatImean?

No. Keep it.

if you have a plug in trickle charger those can rejuvenate batteries if they are having trouble getting fully charged (the altenator is not meant to bring back dead batteries, only top off)