[G80indy]

With paint correction and the amount of time people spend on getting an M car's finish just right after factory delivery /handling and shipping, I'm amazed people put car covers on their cars inside a garage during the winter.

I have a Custom Noah car cover and an external moisture barrier car cover on my Z3 in the driveway, but it's sitting out during the winter so there's a reason for that - not to mention it's an older car.
However I don't want anything touching the paint on my M3
A little dust accumulation can be easily handled in the spring with a little power washing/ foam cannon and spot free.
But to each his own — good luck.
By the way the CTEK lithium charger is great; It will gently raise the voltage on your battery, and then once it's done it will float around 13.65 V. However, I don't know if I would recommend leaving it on, during the winter
lithium-ion batteries don't need to be at 100%. I monitor the voltage of mine with a CTEK voltage battery monitor via Bluetooth.
Look into it— you don't have to guess about the voltage of your car. Mine is holding at 13.35 V — no tender. No guessing. pretty impressive for that battery.