I'm not saying we didn't do it; I'm saying it might not have been the greatest idea in the world.
And in fact, it wasn't. If you'll recall--if you know anything about Beetles--worn rear seat springs and/or heavy rear seat passengers would bounce those metal springs right onto the battery posts.
We did a LOT of things in 1960-1979 that we don't do today, because we know better. You know that, but really don't want to acknowledge that. You'd rather leave it out there that "well, we put batteries under the seat in the Beetle" because it makes it look better that you can take ANY $30 battery and use it in a Prius.
And that was the crux of this whole discussion: your assertion that the Prius is "better" because it can use a $30 tractor battery to open the relays and run the auxiliary electrical requirements of the car. Never mind that you shouldn't; you just want to hang on to "it can".
You can do anything you want, but that doesn't mean it makes sense.