central locking remote doesnt always work
 

hi ive a volvo s70 t5 p reg. when i bought it the remote fob was damaged so i bought a new one and 2 new batteries. i swapped them over but it didnt work at all. so i put the old battery back in the new fob and it worked. But a week later and i sometimes struggle to get the remote to lock the car its ok opening it. Could it be the battery or do these things have to be reprogrammed?

please help
Mark.

It might be a problem with the button inside on the curcuit board.