The first step is to check the panel's status and verify that you have a "System Low Battery".
Note: If your panel is reporting an "AC Power Failure", then you will need to fix the power failure before you troubleshoot the low battery.
Clear System Troubles: Press the "Status" and then the "Disarm" button to erase all old memory in the system.
If the message still hasn't cleared, you can run a "Sensor Test" to try to clear the low battery warning.
Follow the instructions below...
If the previous steps did not clear the "Low Battery Message", or if it comes back again, you can check the battery voltage by holding down the number "6" on the panel. If the battery voltage shows 1.00 V, most likely the battery is disconnected and you will need to check the battery connections. Next, give the battery 24 hours to charge.
If it still shows the "Low Battery Message" after 24hrs, you will need to replace the battery.
If the panel continues to say "System Low Battery" try the following...
1. Make sure your system is Disarmed.
2. Remove the AC power transformer from the wall outlet.
3. Disconnect the 2 red wires in the back of the panel. Plug the red wires in. The unit will power up.
Note: If you can't find the red wires on the back, you will need to open the panel to access them. Open the panel by removing the screw at the top, pushing the 2 white tabs down on the top right and left and pulling forward. You will now see the battery and the rest of the circuit board.
4. Connect the AC power transformer back to the wall outlet.
If you need to replace the backup battery, you can turn off the trouble beeps on the panel while you wait for the replacement. You can get a "new battery here".
The following video will show you how to remove and replace your battery in your Simon XT: