Back to the original question, I would not want to fly any aircraft
without the ability to reliably (i.e. when the battery dies) know and
be able to report pressure altitude.

Darryl

If your battery dies, wouldn't you lose your ability to report
anything to anybody?

I'm not suggesting we fly around without an altitude readout of some
kind, but does it have to be the big, old 80mm round dial? Why can't I
use the pressure altitude displayed in double height on the home page
of my SN-10. Keep the black cursor on it, so my altitude can be read
at a glance. If I should have the SN-10 on another page, I can always
read pressure altitude to the nearest 100 feet off my transponder. If
for some reason I'm unable to use any of the above, I can always read
pressure altitude off the GPS (model 20).
Most of us have two batteries so we can switch if the primary goes
dead.
JJ