How much do you drive? If you had a low/weak battery and simply jumped it to get going then it's possible that you never fully charged the battery. It may have enough volts to test good fo a while but then dwindle out over eight hours of sitting.
The truth is if you haven't added any new electrical compnents lately or re-wired anything then you must have something shorting out. You can verify this by pulling the ground cable off the battery one night. When you re-attach it in the morning and the car starts then you know that you have a constant drain somewhere. Now you have to find it.
It will be something that has constant power. Your sig says that you have a big system. I'd start there. Feel on some of the wiring and compents and see if feel any heat. Heat=power. Check the condition of all the power cables for fraying, pinchpoints, and where they run through gromets or near bare metal.
If you have no luck there then simply start pulling fuses for certain systems over night until you can at least narrow it down.
