If the battery voltage gets too low, your inverter will sound a low-voltage alarm.  This can happen for any of the following reasons:

-The battery is low and needs to be charged

-A loose connection with the battery cables

-A loose connection in the 12V vehicle accessory port (if you are using a 12V power cord)

-The battery cables to the inverter are too small

-The appliance is pulling excessive power from the battery