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That rear hole that you snaked the tube through is actually for the battery hold-down clamp. In the bottom of the well at the front, the tab at the bottom front of the battery slips underneath the hold-down fixed to the well. At the rear, the hold-down is a wedge-shaped bracket that gets pulled down towards that hole, keeping the front engaged and down, rear wedged down.
At the top, your battery came with a couple plastic shields to cover the terminals. Each shield has a couple plastic pins that fit in those little holes in the top of the battery. You'll need to do a little creative scissors surgery to make room for the cables. The forward shield is especially important, as it keeps the battery box cover from welding itself to the positive post. This is particularly critical while your battery isn't clamped down.
+1 on what Dr Bob says. Obviously you have not seen one of my earlier posts on whatever thread but some 16 years ago I was driving along a busy expressway in my late S4 with my family in the car [wife plus two -young at the time- daughters]. I was in the outside of three lanes at night doing about 75 mph and al of a sudden the "lights went out" as in no engine, no dash panel, no external lights, no indicators, no hazard lights, no windows opening and cars everywhere! To make matters worse I was slowing down [obviously] and had to literally barge my way across the lanes onto the hard shoulder and coast to a halt- safely thank goodness.
Opened the hatch, got all the wheel well crap out of the way went to open the battery flap and......NADA! I could see a scorch mark on the paint adjacent to where the positive post was. Had to tow the car home and then drill out the lid to break it free from the welded stud.
Turned out that after working on the car I forgot to fit the hold down bracket, the battery must have bounded over a bump and created an auto arc welding machine in the hatch. Lesson learnt- nowadays I always put a strip of sheet rubber over the top of the positive post as well as THE HOLD DOWN BRACKET!