Ensure the vehicle is unlocked and the driver and front passenger doors are closed.
Install a handset in the ignition switch, then turn the ignition switch to position I and back to position 0 in less than 5 seconds
Press and hold the unlock button. then press the lock button three times within 10 seconds.
Release both buttons.
the doors should now lock and then unlock if repeat with other plips (without switching the ign on) all plips must be done within 30 secs.
and yes as you know you can change the batt, I was thinking of something else.
If both LED's work and the above proceedure won't work with either plip I would look at the RF receiver next.