Re: Active Noise Reduction Headsets
The 'J' version is powered by the aircraft intercom system, so there aren't any batteries. Should the ANR system fail/degenerate (usually just following servicing funnily enough) the headset has an ANR on/off switch to revert it back to an almost standard Atlantic headset. New H+S regs mean there is now a restriction on the number of flying hours each crew position can complete in a year without ANR functioning!
There was a trial to use a battery pack powered ANR in the K (which I remember worked very well until the back end was opened up) but it fell by the wayside after some planker decided it would be cheaper to pay deafened people compensation!