The XL 9 portable battery powered module uses a nine-volt alkaline battery to provide power to David Clarks's headsets with their electronic noise cancellation (ENC) system. From one nine-volt battery, this battery pack provides up to 25 hours of operation. The auto-shutoff function automatically turns off when microphone bias voltage is lost when unplugged or the aircraft audio is system is shut off. A switch inside the battery compartment controls the function of the auto-shutoff feature: disabling auto-shutoff provides continues power to the headset's ENC system whenever power is switched on.
