MG ZR central locking signal

[mlj]

I have a 2005 MG ZR and the signal for locking and unlocking my car seems to be lowering day by day.

I bought a new battery for the fob just before christmas and had been working fine for me, (un)locking from a few yards behind the car.

But, now I have to find just the right spot in the top corner of the drivers side back window, otherwise it won't (un)lock.

Surely it cannot be the battery that has died already? Any suggestions?