They use an SR1120W. Always use a silver oxide variety (which are 1.55V).
It should certainly last longer than a month or 2.
The G757 module is a bit finicky. Try another battery and see how it goes.
There might be some battery residue on the circuit board which is causing excessive current draw.
Or the battery you put in may have been sitting on a shelf for years and had degraded.
I'd suggest trying another battery change to start with.
Rgds.