So alternator...

It's charging at about 9.5 on idle, and it'll reach 13.2 at 2k revs plus. My battery is no longer able to start the thing,

Yep, sounds buggered to me. Rectifiers maybe?

You got a question for us, or just wishing to vent?

Should be higher then that at 2000rpm.

Get it rebuilt or put a Patrol 90 amp Alternator in.

I had a question, seemed to of cut me off? Oh well...

Anyway, it's flicking on and off, meaning it'll be a crappy charge at 9v and maybe reach 12 or 13 over 2 g. But then randomly, all the lights will start working again, the stereo comes back on, and when I check with a multimeter, it'll have 12.5 on idle and 14.1 anything higher than 1g revs. Which is obviously normal. So there's a wire or something playing up. But now I just can't bloody figure it out.

I had an alternator in a car that did that when the brushes were really badly worn and only intermittently made contact. I have no idea if yours has brushes or if it does, if the brushes are replaceable. If they aren't, it's a new alternator you'll be needing and if you have to, get one with higher output - but make sure the rectifier and regulator are included. There's no point getting an alternator that can pump 90A if your regulator/rectifier can only handle 50A.

Other than that, check that the electrical connectors are clean and not corroded. Take them apart and inspect them.

corroded connection on battery is good point, check also for crack on fusible link

I don't know what happened, but it healed itself. Has been fine for about 2-3 weeks now.

Ninja mechanic?

whers the regulator/rectifier on a d21???

look at the back of alternator ? maybe