After you check that the battery is actually charging, you need to find where the draw is. Look for something that has been added like a new radio with amplifier that was wired incorrectly, if it goes directly to the battery I would check it first. Then check your drawdown as it is drawing down at least 400 amps over night, that is a pretty good draw, so I would check each fuse instead of starting the check at battery post. With a full charge disconnect a battery post and watch for a spark when it is reconnected after a few seconds. The spark from reconnecting should be very minor, Using a volt/amp meter (cheap ones from harbor freight work fine) set up for 10 Amp reading (you usually have to move the red wire to a different post). If I remember correctly) there is a set of fuses next to the battery with a wire from the battery that goes to one side of the fuse box. With key off pull one of the fuses and put the red lead of amp meter into the fuse opening fuse slot on same side of where the wire from positive battery post went. Then put the black lead of amp meter into the other fuse slot. Your amp meter should give a very low reading 0.0?. If much larger that is the circuit that has a problem. Check all the fuses one of them should have a reading larger than 4.0 amps (all should have a reading below 0.0 but you have something drawing on it). The cover to the fuse box (if it is still there) will tell you what each fuse goes to.
Good luck, let us know what you find.