battery keeps dying

Not to beat a dead horse, for me personally, it's a bit tough to understand sometimes, so Like the members above said...
Simplified, it's also known as a voltage Draw.
A 12V light works fine.
With the battery already charged. Disconnect the negative terminal and place a test light between the ground cable and battery terminal.
If it lights (dim or bright) then there's a voltage draw.
Disconnect circuits at the fuse panel until the light goes out, to narrow down the circuit causing the draw.
Keep in mind the opened door will also show up as a draw (because the interior light is drawing, but won't be visible since the battery negative cable is off).
And yes, common culprits have been mentioned above.
Let us know on your progress.
(My money is on the trunk light)
Over and out.