I had a similar problem with a Hummer that had a 6 CD changer. One got jammed and it kept trying to cycle through the change even after being turned off at the key. Your radio being on when the key is off is a hint. My 2008 Jeep liberty has many things that stay on when the key is off but supposedly go off when the door is opened. Have a Jeep service shop check to be sure the computer that controls all that type is stuff is functioning correctly.

Disconnect the battery cable when you park for the night until it is fixed, draining the battery down repeatedly will shorten it's life. Look for vanity lights left on, seen 'em before. The shop will place a current meter in between the battery and cable and check the current drain and proceed to pull fuses one at a time to find out what is causing it.

Take it to a mechanic that diagnose a parasitic draw. It is not rocket science. Spark plugs have NOTHING to do with this problem. Expect some aftermarket install to be causing this draw. You are on the right track with this problem.

It might become a problem if you make little mistakes in there. I recommend you to get a consultation with a mechanic. Here, this might help you out http://bit.ly/1vmd8MP

I have a 2001 Jeep Grand Cherokee Laredo. The battery died, so I took it in and had the battery and alternator tested, and both were fine. Several days later my battery was drained again, so I took it back in and my terminals were replaced. Several days after that my battery died again, and my mechanic replaced my spark plugs. It just keeps slowly draining. I've noticed that my dashboard clock never turns off, and that my radio will turn on even without the keys in the ignition, so that might have something to do with it.

Any ideas?