The Interlogix Simon XTi-5 requires a 6V, 2.1Ah alarm battery.

Note: It is recommended that the backup battery is replaced every three to five years. 

To replace the battery in an Interlogix Simon XTi-5:

If desired, put the system in test mode with the monitoring station before proceeding. 

1. Disarm the panel.
2. Power off the panel. 
   1. Remove AC power from the panel.
   2. Disconnect the panel from the mounting plate.
   3. Disconnect the existing battery (A in the figure above) from the battery connector (B in the figure above).
3. Remove the existing battery by reaching under the battery, next to the plastic latch (C in the figure about), with a finger and pulling up.

   Important: Do not try to push the plastic latch back to remove the battery.
    

4. Insert the new battery into the battery compartment and snap into place.
5. Power on the panel.
   1. Plug the battery connector into the panel.
   2. Reconnect the panel to the mounting plate.
   3. Restore AC power to the panel.