Engineers code for galaxy 16 plus?

Just got home and noticed when going to deactivate the alarm that it was indicating power failure and the green power light was flashing fast! This system has not been under contract from ADT for a number of years. On checking the Galaxy manual, this is indicating either a fuse or battery failure, however when I took the fuse out, the control panel stayed on which indicates to me that the battery is ok. Not sure why all of a sudden this has happened, any advice/assistance would really be appreciated thank you.