Sennheiser 502399 Instruction Manual page 14

The operating time with batteries/rechargeable batteries
is approx. 60 hours.
With NoiseGard™ switched on (see page 10), the LED
provides information on the remaining battery/
rechargeable battery capacity.
LED lights up yellow: The battery capacity is
LED lights up red:
Activating the "auto shut-off" function
The battery-saving "auto shut-off" function automatical-
ly switches the NoiseGard™ electronics off when the
headset is disconnected from the audio system or when
the aircraft avionics are switched off. The headset is de-
livered ex-works with the function deactivated. You can
activate "auto shut-off" as follows:
Set the switch to the position ASO.
12
sufficient.
The batteries are flat.
Replace the batteries.