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Reserve Cell Mercury batteries

UWB-300 was a series of high-capacity long-life Mercury batteries, also known as the Reserve Mercury Cell or Reserve Cell, developed between 1962 and 1968 by PR Mallory and Co, 1 (now: Duracell) for the Technical Services Division (TSD) of the US Central Intelligence Agency (CIA). The batteries were made especially for use in combination with covert listening devices (bugs).

The cells should be filled with electrolyte shortly before they are first used. Until that time, they can be stored for at least 10 years without losing their capacity or reliability. The electrolyte is entered through a port at the bottom, that is sealed with a nylon screw. The new batteries were designated UWB-301, UWB-302, UWB-303 and UWB-304, with capacities ranging from 3.1 Ah to 26 Ah (ampere hours). Note that the D-cell is pre-filled with electrolyte and is plunger-activated.

The expertise gained from developing these batteries for the CIA, was later used by Mallory to improve the performance and reliability of batteries for cardiac pacemakers. Mercury batteries were also used extensively in analogue photo cameras, mainly because of their long life and constant voltage (needed for the light meter). Today mercury batteries are banned in most countries, due to their toxic contents and environmental concerns upon their disposal [1].

  1. Although the name of the manufacturer is officially unknown — the report [A] is redacted at this point — it is nearly certain that this was P.R. Mallory and Co Inc.  Read more

The diagram below illustrates the lifecycle of a mecury battery. When it is first activated by filling it with electrolyte (T0) it produces an initial voltage of 1.5V. In the following hours, it gradually drops to 1.35V (T1), where it remains for nearly the entire operational life. For this reason, mercury batteries were also used as voltage references. Near the end of its life (T2), the voltage suddenly starts to drop, until is collapses completely a few hours later (T3).

World War II
The Mercury battery, or Mercury Cell, was invented in 1884 by Charles L. Clarke in Manchester (UK), and is described in US Patent 298175 [2]. It was first widely used during WWII, when US inventor Samuel Ruben teamed up with P.R. Mallory and Co Inc. 1 , and developed the first practical implementation of it for the US Army. It was considered a breakthrough in battery technology. Mallory's batteries were used throughout the war in portable electronic devices [1].

After the war, the heavy Mercury battery was largely forgotten, but a minaturized version — known as the Button Cell — found its way into small electronic devices like hearing aids, wrist watches and cardiac pacemakers. The Mercury battery had several advantages over regular ones: they had a long shelf life (10 years), lasted much longer, and delivered a voltage of 1.35V per cell, that remained constant during its entire life. But there were also disadvantages, the most important of which is that its toxic mercury causes environmental concerns when it is disposed.

Cold War
During the Cold War, the mercury battery was a popular item of the CIA's Technical Services Division (TSD), where it was used to power covert listening devices (bugs). But despite the prolonged life of the battery, there were also a number of problems with them. In 1962, the TSD started a large experimental program in which large numbers of different designs of mercury cells were put on load and discharged under conditions simulating the multi-year low-current drains encountered in use [A]. As part of the program, the following problems were identified:

  • Internal short-circuit caused by free mercury
  • Loss of anode contact due to preferential corrosion
  • Migration of zinc reaction product within the cell (causing shorts)
  • Unreliable PVC separator inside the cell
  • Self discharge
The CIA then commissioned Mallory to develop a new type of mercury battery in which all above listed problems were solved. Mallory addressed each problem individually, and tested possible solutions extensively, before incorporating them in the final cell. In April 1968, the research was finished, with the introduction of four types of The New Battery: UWB-301 thru UWB-304 [A].

PR Mallory
Officially, the name of the company who developed the UWB-300 series batteries for the CIA is unknown. The report, that is available for download below, is redacted at that point [A]. In his book Spycraft however, author Keith Melton et al., describes how the TSD tested a wide range of mercury batteries during the mid-1960s, and how they commissioned Mallory to develop a new type of mercury cell, based on their RM-1, that did not suffer from the known deficiences [3]:

This situation led a small cadre of TSD battery scientists to focus on mercury cell technology as offering the greatest potential for long power-life in a small package. In the mid-1960s, TSD established an extensive battery test program that produced more and better data on mercury cell performance than anywhere else in the government or industry. These testing results led TSD to focus attention on a cell named the RM-1, made by the P.R. Mallory Company, and to create a specialized power sources unit for evaluating commercial batteries and developing smaller, longer-life cells for clandestine applications.
TSD considered mercury cell technology as the most viable solution for clandestine applications (bugging), but had found it to be unreliable when used over an extended period of time – i.e. months or even years – whilst drawing a very low current. The book continues:

TSD studied the failure mechanisms of the RM-1 cell and through a process of identifying failure modes, correcting each one, retesting, and further correction, the RM-1 evolved into a deployable component. Eventually a series called the 'Certified Line' was produced. "That was our certification," noted Linn. "It was certified for sure, certified for CIA's clandestine audio operations."
  1. P.R. Mallory and Co Inc., was founded in 1916 by Philips Rogers Mallory. Although initially manufacturing tungsten wires for filament lamps, Mallory soon became one of the best known battery manufacturers in the world. The company is known today as Duracell.

  1. P.R. Mallory and Co Inc., 1 General Description of the New Battery
    4 April 1968. Via CIA. Not marked as classified.
  1. Officially unknown (redacted) but very likely.  Read more

  1. Wikipedia, Mercury battery
    Retrieved January 2018.

  2. Charles L. Clarke, Galvanic Battery
    US Patent 298,175. 6 May 1884.

  3. Keith Melton, Henry Robert Schlesinger, Robert Wallace, Spycraft
    ISBN 978-0-55382-007-2. pp. 190—191.
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Crypto Museum. Created: Monday 22 January 2018. Last changed: Tuesday, 23 January 2018 - 21:24 CET.
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