Error Code BAT

Low battery condition in a wireless sensor or low system battery.

? What Causes This

Weak or depleted battery in wireless sensor or system backup battery.

✓ How to Fix It

Replace the battery in the wireless sensor with a fresh alkaline or lithium battery as recommended by your installer. If BAT is displayed with no zone number, replace the system backup battery and contact your installer.

Source: page 10 of the official manual

From the manual

This error code appears in:

Honeywell Vista-20P Security System