Headphones working without battery :o I have a pair of qc25 which are awesome when I'm working or travelling (train or plane); don't need wireless when I'm sit

Headphones working without battery :o I have a pair of qc25 which are awesome when I'm working or travelling (train or plane); don't need wireless when I'm sitting. Swapping battery is trivial and if I'm out headset is still usable just no ANC.