Key fob not working after car battery change?

My car battery drained about 30 days ago right before vacation. I changed the battery today and everything works fine. If I walk away for a bit and come back, my wireless entry fob (that unlocks door and sets alarm) does not work until I get to door, and it unlocks by handle. Car starts and everything and then fob works again until I get out of range and then acts like it's dead again until I repeat procedure. What could be causing this?