Mains Failure causes Accenta 8 Problem?

Hi, I am trying to help my mother in law.
She has an Accenta 8 alarm. It has the Main Panel, the Door Keypad and External and Internal sounder. The other day the Mains power failed but came back quite quickly. The problem is the keypad numbers are illuminated but they do not respond when touched. The DAY and POWER lights on the keypad are extinguished but the POWER light is on on the Main Panel.
I cannot locate the power feed/spur and fuse that the Main Panel feeds from. I have powered the Mains down and back up where it appears to be fed from the lighting circuit (on the Mains Fuse panel) but this makes no difference.
I suspect the battery ...any suggestions please?