SL compact alarm?

Hi I have an SL compact alarm system with 3 separate key pads . The problem is there is no red power L.E.Ds lit on any of my keypads but I have the green back lit l.e.ds lit .i have checked the voltage output and is 13 volts at all the key pads , but I can't get anything to work .there,s no tamper or anything ,all the sensors are working and all the fuses are intacked .the battery is flat and the system is on mains supply at the moment. Any ideas thanks