Central Door lock do not work at low temperatures ?

Ford Focus ZETEC 16V 1400ccm 4+1 door - central lock by key
At lower temperatures the key oppens only the driver door not the other doors. Sometimes after i lock the car next morning I find empty batery and the car do not start.
At temperatures higher than ca 20 degrees celsius all doors oppen normaly.
Took of the fuse and disabled central lock, but i would like to know why it is related on low temperature and how to fix the problem.
In the Ford service they told me to change all the locks