I have an 05 just like yours and it works in mine. Check the manual for exact instructions

So how long can the fan run for before it drians the battery?

I have "max ac" on my 2006? I have aux ventilation on my navigation screen and I can set it for certain times, same with my 2005?

Mine has the Max button but nothing happens when I push it. I thought for sure I would have this feature considering I can even program when the fan comes on in my mom's '94 540.

Max only can be used when it's cold. When it hot, you need to program it in the obc to come on instead. Merely pushing it when it is hot does nothing. I have an 05 that works like so. Check the owner manual for details.

In the winter after you shut the engine off, but before you take the key out of the ignition, if you press the MAX button the fan will circulate the residule warm air throughout the cabin. You can also program this using the OBC.

How long does this fan stay on? wouldn't it kill the battery?

I have an 01 with the MAX button.. I need to check it out.

The Owners Manual for my 05 says 30 min.