Legacy Keeps Going Flat

I can't say for sure but I would check for something that is not turning off when you turn the car off. Things I could think of would be like an Amplifier that is connected directly to the battery not through the ignition system or if you have had any stereo equipment installed recently some one may have connected it directly to the battery so it is always on. Another shot in the dark might be something in the cigarette lighter like a penny or something.

Hope one of those works for ya
Good luck :)

turn the car off, go around and check everthing to make sure they are off. if that checks out, the problem may be in the regulater which is in the altinator. have seen the same thing happen when with rebuitl and new altinators. some stores like auto zone do have people to do tests.