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The nomination of battery, cell, has changed a lot over the years.
What is important, is your case is the nominal voltage for the best
operating condition of the Spotmatic. The mercuric oxide battery, as
it is correctly called today is an alkaline electrochemical compound
that delivers 1,35V.
From Wiki…
Product ban
The 1991
European commission directive 91/157, when adopted
by member states, prohibited the marketing of certain types of batte-
ries containing more than 25 milligrams of mercury, or, in the case of
alkaline batteries, more than 0.025% by weight of mercury. In 1998
the ban was extended to cells containing more than 0.005% by weight
of mercury.
In the United States, in 1992 the state of
New Jersey prohibited sales
of mercury batteries. In 1996 the United States Congress passed the
Mercury-Containing and Rechargeable Battery Management Act
that prohibited further sale of mercury-containing batteries unless ma-
nufacturers provided a reclamation facility, effectively banning their sale.
Substitutes
The ban on sale of mercury oxide batteries caused numerous problems
for photographers, whose equipment frequently relied on their advan-
tageous discharge curves and long lifetime. Alternatives used are zinc-
air batteries, with similar discharge curve, high capacity, but much shor-
ter lifetime (a few months), and poor performance in dry climates; alka-
line batteries with voltage widely varying through their lifetime; and sil-
ver-oxide batteries with higher voltage (1.55 V) and very flat discharge
curve, which makes them possibly the best, though expensive, replace-
ment after recalibrating the meter to the new voltage.