Originally Posted by S10 Racer
Unless you have something draining the battery (stereo, amp, etc.) or the battery is getting old, it should not discharge while setting. You need to find out what is draining the battery.
This is the right answer. With the right tools if there is a draw you should be able to pin it down is short order. Its not hard you just need to be methodical. I good quality amp meter is the key to locating this type of issue.