The job of the battery is to start the vehicle. Once that is done, the alternator takes over. The alternator not only works all the electrical things in the vehicle, it also gives a charge to the battery while the vehicle is running.
So, if your vehicle is not staying charged overnight, it has to do with the battery. If you can jump it in the morning and all it fine, then there is probably a draw on the battery somewhere in the vehicle.
If this just started then I would look at anything you did recently to the vehicle. Did you have anything new installed that uses electricity?
Is there a light on somewhere after you turn off the key? A dome light that stays on, a trunk light, a door light...these are the little draws that kill the battery overnight yet allow it to be jumped with no problem the next day.
If you can't find the problem yourself, then I suggest that you have a technician test the battery and do a draw test. Hope this helps.
〉 Answered on May 4th, 2008 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines