UPDATE: After confirming with Bose®, the Bose® QuietComfort Ultra 2nd generation is also useless when the battery goes flat. 

Last year we decided to stop manufacturing the Avee for the Bose® Ultra.
The design of the Bose® Ultra and the 2nd generation,  sadly, makes it unsuitable for aviation purposes – and even recreational purposes.

The Ultra has a good ANR and excellent comfort, but it does not work when the power is off or the battery goes flat.
The “no work when no battery” feature is even a problem when using it on long flights as a passenger and being connected to the aircraft entertainment system via a cable: the headset simply stops working when the battery is flat.

There are far better and more affordable solutions available that we do support: the Bose45/SE/SC/QuietComfort and the Sony XM3, XM4, XM5 and XM6.