Mercury
When mercury batteries were about to be proscribed, I went out and bought a
lifetime supply, and keep them in the freezer. The photo magazines all
claimed that freezing batteries doesn't extend their shelf life, which is
simply incorrect. I suppose they knew better but were trying to discourage
hoarding, but I wasn't quite ready to put my best cameras and lightmeter in
landfill.
How do I know that freezing helps? For one, this is a traditional approach,
applicable to all battery types; this was common knowledge in my childhood.
For another, the battery handbooks from the various manufacturers also said
that freezing helps a great deal. For example, section 11.5.5 (on the storage
of zinc/mercuric oxide batteries) of the Handbook of Batteries (3rd edition)
states that storage at down to -20 degrees centigrade will, as with other
battery systems, increase storage life. No specific numbers are given. The
limit is that the barrier film between anode and cathode eventually dissolves,
but this takes many years.
The 2nd (1995) edition of the Handbook of Batteries showed shelf life versus
temperature down to -60 degrees centigrade. I'm still looking for my copy of
the article on mercury batteries where this plot appears. A lot of information
on mercury batteries disappeared between the 2nd and the 3rd editions, likely
because they don't want to spend space on a battery type that can no longer be
made.
Silver
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.
Joe Gwinn
Ref. "Handbook of Batteries", 3rd edition, David Linden and Thomas B. Reddy,
McGraw-Hill 2001
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