Battery runs down replaced alternator and starter

Did battery pass a load test? Have you checked for excessive battery draws?

Curiously, a lot of people have reported this battery drain condition due to interior lights staying on and to an electrical short in the CD changer that's located in the trunk. If you don't drive this idiotic car for three days, you're going to have this condition. Rather than getting into extreme expenses, try pulling the CD player fuse, and/or getting an inexpensive Battery Tender, they're about fifty bucks and can save you this trouble.