01 impala keyless issue

I have just bought a new key fob (thought mine was dead) went to program it and it worked. For a while, then the car will not repsond to it. I go back to the settings, resync it and it works again for a while and then quits. Where do i go next?

Maybe the fob battery is dead?

* Keeping it in your pocket or bag may keep the buttons pressed, killing the battery in short order.

brand new battery..