It's PTT on a 737, but you can easily communicate free voice which is what we do.
The Telex 850 does not use batteries either. But when I had the headset upside down and pushed gently on the earpieces to get it in my bag, it snapped the rotating hinge that the earpiece rotates on so easily I could not believe it. Check the Telex website for customer friendliness (not). I have no idea how the Sennheiser fares and whether it is stronger.
You certainly only want a lightweight headset- do not go for the heavy full cup type ones.