Joe wrote about silver oxide batteries:
>>
Section 12.4.3 (on the shelf life of silver oxide batteries)
plots shelf lifetimes at various temperatures, the lowest being 21 degrees
centigrade, but one can extrapolate. The low-rate cells used in watches can
easily last 10 years at 21 degrees centigrade (room temperature). Our
beloved 357 battery is considered ultra high-rate (it's a matter of battery
cell construction). High-rate cells will lose 30f capacity every three
months at 21 degrees centigrade. In three years, the total loss will be 10%.
I guess that ultra high rate may lose more. At 4.6 degrees centigrade, the
loss rate is 0.65 0.000000e+00very three months. Anyway, the max shelf life
they talk
of is ten years for low-drain, and three years for high drain cell
constructions.
As with mercury batteries, the ultimate limit is that the barrier film
between anode and cathode eventually dissolve, and also the silver migrates.
<<
That data from the "Battery Bible" is now a bit out of date. Seals and
seperators have been greatly improved so the differences between KOH cells
and NaOH cells are no longer an issue for reputable vendors.
The performance of Silver Oxide batteries has greatly improved over the years
depending on vendor, so for example the Everready/Energizer Brand 357's
actually have a demonstrated shelf life of 10years in both actual and
accelerated aging tests. Vendors sometimes claim more like 2-3 0a loss at
21C. It is often a variable rate over the cell life and because of impedance
issues (see below), it depends a lot on how you run the test. The Energizer
cells have a lower rated capacity than some vendor's but a lower rate of
capacity loss and a more stable impedance, so probably achieve better
performance despite the lower capacity.
Certainly reducing temperature will help in the normal way as with most
batteries but the seals are damaged by stiffness/contraction at very low
temperatures (particularly if the temperature cycles when you open the
freezer door!), and condensation+salts cause surface leakage. So don't push
your luck. Remember dropping the temperature only 15C (refrigerator
compartment ) will more than double shelf life.
Generic cells and vendors who aim mainly at the watch market , may have
higher capacity loss more like that referenced by the battery bible.
Renata brand for example sells mainly into the watch market and it's cells
have a much higher specified rate of capacity loss at least in the first year
or two.
A bigger problem for some manufacturers is that the cell impedance at partial
discharge increases substantially (2-3 times) after a year or two at room
temperature. This causes the cell voltage of a "new cell" to drop at peak
shutter load (and say ~100se) and can cause camera lockup. Interestingly
the cell impedance drops after further use but the frustrated user will have
tossed it out before that happens!
Somebody else wrote:
>>>
By the way, guys, mercury bio-accumulates. That means that if you are
exposed to trace amounts over long periods of time, your body stashes it
away in your bone marrow. I don't endorse hoarding mercury batteries.
Mercury poisoning is a terrible way to live and die.
<<<
Even the Silver oxide batteries have some amount of mercury in them, just a
lot less.
The flourescent lights probably are the main offenders domestically for
adding mercury to the environment, Don't store them in your refrigerator!
Regards,
Tim Hughes
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