if there’s no number showing the same time the “batt” signal is on the keypad and it’s beeping the system battery needs to be replaced regardless of it’s voltage. the voltage may be ok, but the amperage may not be. if a number shows on the display, it is the wireless sensor associated with that zone. either way the panel will beep every 4 hours to remind you the battery is low until you change it. radio shack is the best place to find the batteries.