1-if you replaced the battery and still not working the circuit board inside the remote probably went bad not sending the RF signal necessary to lock and unlock the door .
But lets try programing it if you have not so far,cause it does need programing after battery removal?
Key fob programing procedure
1-make sure all doors,hood & trunk are closed
2-Insert key into ignition
3-Trurn key to position #2 and back off at least 5 times within 10 seconds ( this is important within 10 secs)
4-The LED indicator should start to flash, leave ignition to on position
5- once the indicator start flashing you have 15 seconds to program remote
6- Press the lock button on the remote .
7- The indicator LED will light up for 2 seconds acknowledges the programing
Please let me know
ASE Certified Technician