How about this:
Every time you hit "download" on a map, we remember this, automagically adding them to favourites.
At the top of the screen, there will be a button "favourites", which shows the list of favourites and a "download favourites" button, which does just that.
You can also "swipe to delete" on the favourites list.
The advantage of doing "auto favourites" is that we don't need to add any new buttons to add favourites and clutter up the interface.
So at the next map cycle, you can quickly download all the same maps you downloaded this time.