DSC PC2550 all Zone lights on

Answer 1

The DSC PC2550 can be programmed for open or closed loop.  Closed loop uses end of line resistors.  you may have lost the programming when the battery went dead.  Installation and programming manuals are available on-line.  Verify what you have and start from the beginning reprogramming it.  It isn't very user friendly and was designed for installer's job security.