A set of alkalines will go for a few months.
Your remote will start beeping at you one day while you're flying and you'll think WTF?
But you still have plenty of life to allow you to safely bring the Phantom in.
Just carry a set of spares in your flying box.
IIRC using a good set of alkaline batts. (CopperTop, etc.) worked out to ~20 hours.
Don't be concerned about range as the batts. age. The controller has voltage regulation that assures full RF output power until prompted to replace the batts. by the internal alarm.