It was definitely the siren batteries. Once removed, the battery has not died once nor have the lights been seen flashing. I am once again gaining confidence that I can go to my car and it will actually start versus being met with a dead battery.
I have received the batteries and will wire them into the siren, reassemble it and install when I get time; I'll try to post pics to help explain.
Hope no one else has to go though this, but if they do, at least there will be a post to help them.