Mercury Battery - Substitutes

Substitutes

The ban on sale of mercury oxide batteries caused numerous problems for photographers, whose equipment frequently relied on their advantageous discharge curves and long lifetime. Alternatives used are zinc-air batteries, with similar discharge curve, high capacity, but much shorter lifetime (a few months) and poor performance in dry climates, alkaline batteries with voltage widely varying through their lifetime, and silver-oxide batteries with higher voltage (1.55 V) and very flat discharge curve, making them possibly the best, though expensive, replacement after recalibrating the meter to the new voltage. Special adapters with voltage dropping Schottky or Germanium diodes allow silver oxide batteries to be used in equipment designed for mercury batteries. Since the voltage drop is a non-linear function of the current flow, diodes don't represent a very accurate solution for applications where the current flow alters significantly. Currents drawn by old CdS light meters are typically in the 10 µA to 200 µA range (Minolta SR-T range). Various kinds of active voltage regulation circuits using SMD transistor or integrated circuits have been devised, however, they are often difficult to integrate into the battery compartment space. Replacements must operate on the low voltage of a single cell. Lack of a power switch on many old light meters makes an ultra-low-power design mandatory.