Causes Battery drains when parked?

any short or electrical issue. You need to test each electrical circuit for a parasitic draw. youtube has some videos to get you started if you want to find it yourself.

How long is it being parked? If less than about two weeks, follow TDolby's advice. If the vehicle is being parked for more than about two weeks the battery is going dead because the vehicle computers are still drawing a small amount of power from the battery. A battery tender will help prevent the battery from dying when you park the vehicle for an extended time period. Hope that helps! Jim