Richard Muin writes:

There are at least a couple of "new improved" versions. I would look
for the small AA battery holder to know that it's the newest one of
which I'm aware.

maybe sb. can give me a picture of the battery holder. at bose.com there is
no pic available... :-(

No picture should be necessary. Either it takes a 9V battery or (1.5V) AA
batteries. (If it takes a 9V battery, the next thing to check is the head
strap. The newer ones have a patch of wool.)

I think there is a picture in a recent Flying magazine though.

--kyler