Energizer PP355 - Manual (Page 12)

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ENERGIZER BATTERY MANUFACTURING
VERSION 1.2
Section 3: Application and Design Considerations
Excessive exposure to air can have an adverse affect on Zinc Air battery operation, primarily due to
carbon dioxide reacting with the electrolyte in the air electrode. The battery can also absorb water or
dry out depending on ambient conditions. Balancing the air requirement of the battery during discharge
versus the need to minimize exposure during rest is called air management. Air management might be
as simple as removing the tab from the battery and inserting it into a device, or it might include a system
to open and control air access to the battery as needed. Air management is application specific, and
most devices will require some degree of air management to optimize battery performance.
3.1 ‐‐ Air Management
There are several types of air management. The simplest method of air management is removing the
tab and putting the battery in the device. This is how miniature zinc air cells are used in hearing aids
since the total battery life is typically expected to be 6‐8 weeks. As the device usage becomes more
intermittent, other methods of air management are needed to deliver optimal battery performance.
Throttling is a technique to permanently restrict air access to only what is needed by the battery in a
specific application. Throttling is most appropriate in devices that require a small portion of the
maximum current that a battery can sustain. For example, a device might require 10 mA of current
compared to the maximum of 100 mA that a PP355 can sustain. This technique works best for devices
that have a low average drain rate with little increased power needs. By restricting the air access to the
battery, the performance life can be extended.
As device use becomes more intermittent and as device power demands increase, valved (open and
shut) air management becomes more appropriate. Valved systems are either mechanical or electronic.
Each system requires a sealed battery or battery compartment, into which air is introduced by the valve
when the device needs power. A seal can be accomplished with common materials such as o‐rings,
gaskets, over‐molded or two‐part injection molded materials, or other methods. A mechanical solution
might be an ON / OFF slide switch which acts as a simple air valve. Other device specific mechanical
actions could also be used to open and close the air access. Examples include changing device settings,
moving a piece or a part of the device during use, pressing a button, turning a dial, or manipulating a
threaded component. An electronic valve would act in a similar fashion, except that the device
electronics would open the air access automatically. A valve could be opened as a function of device
state (on = open, off = closed), or it might be a function of the instantaneous power needs of the device.
In a valved air management solution, a low level of air access might still be needed to be able to provide
the quiescent, or background, power required to activate the ON/OFF valve. Figure 11 shows generally
where each of these air management techniques is appropriate.