So my car was dead and I assumed I needed a new battery. New battery is loaded in and the car runs like a champ. Today I went to start my S and it's completely dead. How do I find out what is the culprit? Any insights are greatly appreciated. Thanks

 

Maybe the alternator is dead which is why it zapped the battery. I'd yank it, bring it to the local parts store and then have them test it.

 

check the fan belt first -

then the alternator -

or it could be something that's draining your battery ie maybe a door light / trunk light, etc etc

will it fire up with a jump?

 

Yes my car fired up with a jump. It's currently on a trickle charger and I disconnected the stereo power from the battery. I'm hoping I messed something up when I redid my stereo

 

JS---do you have a small radio shack volt meter?

Charge the battery and start the car.
Put one of the tester to black battery ground and the other to the positive.
Idle the car and raise the rpm....the voltage should start climbing from 12 to 13v and more.
If the the voltage is not 13 while raising the rpm, the alternator is dead.