Battery

My son has a 1990 ford taurus 3.0 with 150,000 miles on it. About a month ago we had to start disconnecting the battery or it would not start after sitting. Then the battery started leaking acid out of it so we replaced it. It started fine for a few days then we had to jump it again. So then we had the alternator checked, it was bad, and we replaced it. Still no luck he still had to disconnect. The new battery is only 1 week old and it started leaking acid again. Any ideas what it could be?