Tons of Condensation in my trunk

[Quincelady]

Hi Everyone,
I am new to this site and look forward to spending lots of time learning tricks of the trade here :>)
I have a 1996 Mercedes C280(4dr). I was having problems, battery kept going dead after parking it for a week or so. I am not working right now so taking it to a dealer or mechanic is not possible. So! I disconnected the red wire from the terminal after parking it.
Recently after I park it for a few days I find alot of condensation on the "innerside" of the rear window and alot of condesation in the trunk. Everything gets soaked.Even my spare tire gets wet!
If anyone can offer any "insight' on what may be causing this and how I can fix it myself(handy with tools) please, please, please HELP.

Thank You Kindly,
Quincelady