Something is draining your battery when your vehicle is sitting overnight. Have you had anything installed in the vehicle recently? A stereo, NGS etc?
If not, then the next thing to check is the trunk light, if you have one, make sure it's not staying on or that all of your interior lights all are off. Even an interior dome light that stays on all night can drain the battery.
If it's not anything obvious, then you'll need to have a technician diagnose the battery drain. Good luck.
〉 Answered on Dec 15th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines