The only issue is that a continuously low battery is going to have a shortened life due to sulfation, which occurs when the battery is held below 80% of full charge. Since you are not in a garage, you might consider picking up a solar charger that can be left on your dash or rear deck. If you do this, you will have to pull some wires directly from the battery under the trunk floor since all the power outlets cut off about 8 minutes after shutdown. This idea could easily resolve the issue for you and is not too hard to implement.
2012 535ix Space Gray, Cinnamon, SAT, Premium, Prem sound, Cold W., Sunshades, Gloss Black Grille, Gloss Black Side Markers, RE970AS 245/45/19 non-run flats that run very smooth + quiet and also correct the otherwise optimistic speedo