Could possibly be an audio install problem, maybe, possibly? If everything was working ok lastnight, and the battery seemed almost gone this morning, something could be putting a small, constant drain on the battery... even when the car is off. There is a wire from the head unit that needs to attach to a power source to keep all its presets "held" in memory. If that or another wire is wired incorrectly to your power source it could just pull energy from the battery as the car is sitting overnight.