DoN. Nichols wrote:

(...)

It implies your best choice is a type 675 battery at $1.31 each in the
6 pack.

Hmm ... except for the following footnote:

*** Does not account for zinc-air batteries limited lifetime due
to exposure to air

The way mine would get used, the cells would probably die
between jobs.

What if you stored your calipers in an argon - filled
tin? It takes only a couple minutes of air exposure to (re)activate
the cells. I wonder how close you could get to the sealed self
discharge loss of 2% per year...

A few extra holes in your new holder and the battery door?
Piece of cake.

And, of course, he is testing them for use in camera metering
systems -- would probably work in the Nikon Photomic metering finder, or
in the old Miranda spot meter, but not sure about the digital caliper,
which I think has a greater current (it is running at least two LEDs as
well as the photocells and comparator circuits and counters. (I really
should set up a bench supply to provide 5.26V and measure the current --
both when active and when shut "off". This will tell me what I can get
away with. But it is too cold in the shop right now to try that. :-)

Spec sheet says 600 mAH at 2.0 mA rate. 300 hours use per set if you
break it up into 12 hour days. Like 3.5 weeks? Not too bad for less than
6 bux per set even if you never store the batteries in an oxygen - free
atmosphere.


Two 3V cells in series with a silicon diode (typically 0.7v
drop, and I need 0.64V drop -- *if* I make a new battery holder for the
system.

Not too efficient. 2.5 mW wasted out of a 12.6 mW power source.
(Positing 2 mA usage until we know better).
That's almost 20% down the tubes.


Cell dimensions:
http://www.duracell.com/oem/Primary/Zinc/675.asp

That would require making adaptor collars for each of four
cells, because the holder holds four cells, and depends on the bulge
ring to make contact to hook them in series. Or -- perhaps I should
consider making a new holder. (I really should take a few close-up
shots of the holder and post links to them.)

Yes. You Should.

I think that I would prefer two 3V cells and a silicon diode in
series to the zinc-air cells, which start dying the moment you energize
them by pulling off the sealing tape. (The cells have to be exposed to
air to start them working, and they don't stop until they die.)

I'm like that too.

--Winston