If you can articulate a reasonable fear of death or serious bodily injury, then you should be justified in using deadly force. But you must be able to articulate it. In my opinion, someone burglarizing my house is an immediate threat to my family's well-being...therefore deadly force is justified.
It will also depend largely upon the particulars of the situation. For instance, a small male about 5'5", 140 lbs, wanders into my home unarmed at 3 pm. I (6', 200 lbs) am home alone. Barring any other threatening actions on the other guys part, deadly force would be hard to justify.
On the other hand.......
Very large man (6'5", 300 lbs) wanders into my home unarmed at 3 am. I am home with my wife and three small children. Completely different story. I could easily articulate the need for immediate deadly force to stop the threat.
Also remember, you don't shoot to kill AND YOU NEVER SHOOT TO WOUND. You shoot to "stop the threat". It may sound like semantics now, but it may mean the difference between being justified and jailtime. We shoot center mass because that's the way we are trained. It's the easiest target, since it's the largest. If they happen to die, so be it. It is not our intention to kill.
Even more, you never shoot to wound (this bears repeating). If you shoot to wound, then you were obviously not in imminent fear of death or serious bodily injury, therefore deadly force was not justified. You will go to jail and lose everything in a civil suit.
A bat or any other weapon can be construed as a deadly weapon. Guns aren't the only weapon capable of inflicting death. If you would be justified in using the bat to "disable" him, then you would be justified in using a firearm.
Now if you are IN the car, that's one thing. But remember that as a private citizen, you have an obligation to retreat from the threat (except in your own home), and must do so if possible. Someone breaking into your car in the driveway while you are in the house represents little to no threat to you. If you exit the house and confront the POS, and it escalates, you may be held partially responsible.
Lastly, self-defense laws often vary from state to state, so it would be best to consult an attorney specializing in these types of cases in your state.