So I bought the car a few years ago, and about a month in I got a new job and a company vehicle so the car sat Mon-Fri. That's when I realized I had a problem. The battery was drained after sitting. I started just disconnecting the battery throughout the week and that worked fine for a while. Then it started draining overnight if I left it connected. So now I disconnect anytime I let it sit for more than a few hours.

Also, I got a check engine light anytime I start the car for the second time (after I connect the battery) p0420 - p0132 - p0135 - which is O2 sensor related, I don't remember exactly what it said. But it only shows after I crank the second time. I wonder if the two are connected..

Side notes:
-CD changer cycles and makes weird noises as soon as I connect battery??
-I only have valet key/no fob (I have wondered if it's not fully disabling the immobilization security feature)
-front 12V outlet is not functioning..(I haven't addressed this)

Sorry for the long post, it's a long story.. any advise would be great!

 

I don't know what is causing the drain on the battery. You should fully charge the battery, then have it load tested to find out the amps available in your fully charged battery. If the battery tests good, then you'll have to figure out what circuit is drawing current. If the battery is bad, then replace. If the parasitic draw killed the battery, then you'll still have to find the source of the parasitic draw.

 

https://www.innova.com/blogs/fix-adv...P-ac-89N1fzBNI
If battery tests ok try this see if you have a draw in system

 

have you checked if the alternator is working properly? sometimes it can cause weird draining problems.