A lot of people will find their circuit board is covered in green corrosion when they open it up. A lot of the problems with the alarm seem to stem from these batteries going flat and leaking causing corrosion. It needs to be cleaned up before replacing the batteries otherwise some problems will reoccur. I used a different approach on replacing the batteries and instead went for having a separate battery pack mounted remotely from the siren. I did a brief write up on how I did it a while ago.

Matt