My installation went fine and system has been working fine for 2 months now. Yesterday we had a power cut and the alarm went off immediately. On investigation I found that the battery fuse was blown and that the charging circuit was generating no voltage at all.

This means voltage from the supply side of the fuse holder is not present. The low voltage AC supply from the transformer is ok.

If I put in a new fuse ( all I have at home is 1A ) and then connect up the battery the fuse blows immediately.

The open circuit voltage on the battery is around 12.5 volts and I imagine that is the charge it had when I bought it. The battery is not a short circuit .

If I ignore the back up battery circuit the alarm continues to work normally.

As I am unable to detect any voltage being generated in the charging circuit I have come to the conclusion that there is a fault on the PCB or one of its components.

Does the fuse blow when the battery leads are disconnected from the pcb?