Press the status button and once your panel starts talking press the disarm button to erase all old memory in the system. Then press the status button and it will tell you what the current status of the panel is.
For a low battery- If you have recently purchased the system and it hasn't been plugged in for more then 12-24 hours then it still needs to charge the battery. Hitting status will stop the trouble beeps for the next 4hrs.
If it is not a new system and it says system low battery then you will most likely need to replace the battery. After ordering a replacement battery, power the system off by unplugging AC power and disconnecting your old battery. Matching the colors up, connect the new battery. Now plug the AC wires in. Allow 24 hours for the new battery to be charged by your Simon XT.