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 CIA 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 .
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
The Mercury battery, or Mercury Cell, was invented in 1884 by
Charles L. Clarke in Manchester (UK), and is described in
US Patent 298175
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
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.
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].
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 :
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
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
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.
Officially unknown (redacted) but very likely. ➤ Read more
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