The Interlogix NX uses a 12 VDC 4 or 6.5 Ah backup battery. 

To replace the batteries in an Interlogix NX:

If desired, put the system in test mode with the monitoring station before proceeding. For more information, see Put a system On Test with the monitoring station.

1. Disarm the panel.
2. Power off the panel.
   1. Unplug the AC power transformer.
   2. Disconnect the backup battery.
3. Remove the old backup battery. 
4. Power on the panel.
   1. Connect the red and black backup battery leads to the lugs on the panel.
   2. Connect the other ends of the backup battery leads to the battery terminals.
   3. Plug the transformer into an outlet that is not controlled by a switch.