| Title II of the Mercury-Containing and Rechargeable Battery Management Act, signed in 1996, specifically prohibits the sale of any alkaline manganese (except for button cells containing up to 25mg mercury) and zinc-carbon batteries that contain mercury that was intentionally introduced (as distinguished from mercury that may be incidentally present in other materials used to produce these batteries). This act also prohibited the sale of button cell mercuric-oxide batteries. Information is provided below for educational purposes regarding this battery type. For more information on the history and issues surrounding mercury batteries, we recommend the EPA booklet Implementation of the Mercury-Containing and Rechargeable Battery Management Act (EPA530-K-97-009). An on-line copy of this booklet can be accessed via the EPA homepage at: http://www.epa.gov/epaoswer/osw/non-hw.htm#battery.
 The Mercuric Oxide battery was used for applications that required a high energy density and a flat voltage curve. Typical applications were hearing aids, watches, calculators, electronic cameras and electronic measuring instruments. Two types of Mercuric Oxide batteries were available. One type, with a sodium hydroxide electrolyte, had a near constant voltage at low current drain, ideal for electronic watches, calculators, and hearing aids. The other type had a potassium hydroxide electrolyte, which provided a near constant voltage at higher current drains. This second type was used to meet the high pulse current demands of electronic cameras with flash, and watches with back lighting. Cells with a mercuric oxide cathode system were particularly useful where greater terminal voltage stability was needed.
 The current delivery of Mercuric Oxide batteries was determined by the type of electrolyte. The potassium hydroxide (KOH) electrolyte offered less resistance to current flow, especially at heavier current loads. It also allowed the cell to operate at a greater efficiency than the sodium hydroxide (NaOH) electrolyte. The chart at left illustrates this efficiency difference.
 A Mercuric Oxide cell with a mercuric oxide cathode would have an open circuit voltage of 1.35 volts and a very flat voltage discharge curve. This cathode chemical construction was used for watches, photographic meters and as a reference voltage standard in measurement instruments. A Mercuric Oxide cell with a mixed mercuric oxide/manganese dioxide cathode would have an open circuit voltage of 1.4 volts and a more sloping voltage curve. Cells with this construction were often used for hearing aids and electronic measurement instruments. The chart at left shows a comparison of the two cathode systems.
Mercuric Oxide batteries with a potassium hydroxide (KOH) electrolyte would operate at low temperatures with less loss of efficiency than with a sodium hydroxide (NaOH) electrolyte. |
