Starter balls are always available at the beginning of a round or, during a round, after your Premium balls are gone. Premium balls do have a durability rating...in other words, they have a life span and wear out. You can check that rating in the Pro Shop. Besides wearing out, you can lose Premium balls by hitting them OB, into a water hazard
and sometimes in the weeds. When a Premium ball is lost, it is gone forever and the auto caddy will issue you a new Premium ball...this continues until the round is complete or until all your Premium balls are gone. Before you start a round, you may select any ball (including Starter balls) available in your inventory. There is more info available in the FAQ Home over there--->
Joey