The system will switch between them, choosing which is best at the time. In addition to the battery, it could turn recirculate off with high humidity in the cabin.
I've found if I've chosen Auto and pushed the AC button, it'll sometimes switch to recirculate for the first few minutes (dash indicates the switch to recirc too), then back to outside air. I'd concur, recirc is for special occasions, either to accelerate AC cooling, or due to stinky diesel in front.
