I leave both of my Roadsters in the garage for 5 to 8 days quite often.

No issues at all, but then, one battery is a month old, the other 16 months old and are big (in a Reserve Capacity, Amp-Hour and CCA way).

These cars (and really all cars today) will show up to 200 mA current draw just sitting there, there's a LOT of electronics in cars today! If your battery is old and weak, it is NOT going to tolerate being bled down for days and days.

You can always take one of the battery cables off and insert a milliammeter and see how much current is being drawn. If it's over about 150 milliamps, go looking for the cause -your first stop should be the trunk light.