Assuming your cars look like these, you are correct about removing the socket head
of battens depends on the type of fittings. Usually there will be an adjustment screw that you can back off, and slip one end out of the fitting. My old sail had the adjusters at the leech while the new sail has them at the luff.
If you ever need to remove the cars, there should be a short piece of track in your spare parts
. Remove a small piece of track and insert this spare piece. Slide a car onto the removable piece and take it inside where you won't lose the Torlon balls. Cover the back of the car with tape to prevent the balls falling out, and then do the next car.
Edit: Travellerw responded with a different system while I was putting my response together.