2001 MR2 SPYDER.... battery is draining somehow....

Is it possible that jumper cables or cables from a battery charger have been connected to the battery "backwards"? (i.e. positive lead to negative post). When this occurs, even if the ignition was never "on" during the event, it is entirely possible to fry the diodes in the alternator. This can happen to any make or model car. Diodes allow current to flow in a designated direction. when they fail, current flows in either direction causing a parasitic drain. A cheap test would be to leave the battery connected, disconnect the power lead at the alternator for the time period it usually takes to kill the battery (perhaps a week).Reconnect the power lead to the alternator. If it starts, there's the culprit. You can disassemble the alternator and replace the diodes but less hassle to replace the entire alternator (IMHO).

Lets see "alternators" came about in the early 1960s before that it was generator. In Volks Wagon speak its still generators by the way. At lease in the factory service books for a 1995 eurovan.
I degress, what I like to say us in those 60 years the only alternators I replaced on my cars were due to failed bearings. Replaced many on other folks car with fried electrics.
I must live right: I do perverse things like keep clean tight cables. Never, never, let my battery draw down past 40%. 60 % is bad enough. And think of an alternator as a battery maintainer not charger. Heavy duty alternators are a good idea where there's a heavy draw like winches, plows, and, by the way what the hell, do those 10 billion watt sound system monsters draw?.
Honest not a single alternator fried in 60 years. Be nice to your car and go clean your battery cables right now. If you forget to turn off you lights (ect) charge it with a charger not the cars alternator.

Bearings do fail, and the only time that I remembering that happening is 45 years ago on my Fiat x19. The common failures are regulators and brushes. The brushes are an expendable with a pretty decent lifetime. The regulators are a crapshoot, like all other electronics. If you have never had one fail, then I salute your good fortune. Electronics failures are usually just water or oxygen creeping in along the lead seals, or an electrolytic capacitor. Diodes can fail for no reason, but abuse makes it much more likely. I think that I see the point about reversed jumps. Many owners don't even know that they have fusible links in their battery cables. You hear all the time, "I didn't have any electric at all, and it turned out that this crummy piece of wire in the battery harness burned out. I spliced it up, and made good and sure that it won't happen again!"

I was startled to see the word "generator" in the BGB. I think that what has happened is that the commutated generator has been officially declared extinct, and thus there is no longer a need to distinguish between the old and the new. The alternator was not possible until silicon diodes were perfected, but once they existed, they were so clearly superior that this evolutionary outcome was inevitable.