Patent Publication Number: US-6660418-B1

Title: Electrical device with removable enclosure for electrochemical cell

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 09/215,879, filed Dec. 18, 1998, now abandoned and of U.S. application Ser. No. 09/094,924, filed Jun. 15, 1998, and now U.S. Pat. No. 6,068,944. Both such applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to batteries, and more particularly relates to air managers for metal-air cells. 
     BACKGROUND OF THE INVENTION 
     Metal-air cells have been recognized as a desirable means for powering portable electronic equipment such as personal computers and camcorders because such cells have a relatively high power output with relatively low weight as compared to other types of electrochemical cells. Metal-air cells utilize oxygen from the ambient air as a reactant in the electrochemical process rather than a heavier material, such as a metal or metallic composition. 
     Metal-air cells use one or more oxygen electrodes separated from a metallic anode by an aqueous electrolyte. During the operation of a metal-air cell, such as a zinc-air cell, oxygen from the ambient air and water from the electrolyte are converted at the oxygen electrode to hydroxide ions and zinc is oxidized at the anode and reacts with the hydroxide ions, such that water and electrons are released to provide electric energy. 
     Metal-air cells are often arranged in multiple cell battery packs within a common housing to provide a sufficient amount of electrical power. The result is a relatively light-weight battery. A supply of air must be supplied to the oxygen electrodes of the battery pack in order for the battery pack to supply electricity. Some prior systems sweep a continuous flow of fresh air from the ambient environment across the oxygen electrodes at a flow rate sufficient to achieve the desired power output. Such an arrangement is shown in U.S. Pat. No. 4,913,983 to Cheiky. Cheiky uses a fan within air from the ambient environment to the oxygen the battery housing to supply the flow of 1 electrodes. When the Cheiky battery is turned on an air inlet and an air outlet, which are closed by one or more “air doors” while the battery is turned off, are opened and the fan is operated to create the flow of air into, through, and out of the housing. Thus, the air doors are closed when the battery is turned off to isolate the cells from the environment. Although the mechanical air doors may limit the transfer of oxygen, water vapor, and contaminates into and out of the housing, such mechanical air doors add complexity to the battery housing itself and, inevitably, increase the size and cost of the overall battery pack. 
     In contrast to the nonrecirculating arrangement of Cheiky, U.S. Pat. No. 5,691,074 to Pedicini discloses a system in which a fan recirculates air across the oxygen electrodes of metal-air battery. The fan also forces air through one or more openings to refresh the recirculating air. The cells provide an output current while the fan is operating but experience minimal discharge while the fan is not operating and the opening or openings remain unsealed. That is, the Pedicini metal-air battery has a long shelf life without requiring operation of air doors, or the like, to open and close the opening or openings. The opening or openings are sized to restrict air flow therethrough while the opening or openings are unsealed and the fan is off. 
     The restrictive air openings of Pedicini, as well as the air doors of Cheiky, function to substantially isolate the metal-air cells from the ambient environment while the battery is not operating. Isolating the metal-air cells from the ambient environment while the battery is not operating increases the shelf life of the battery and also decreases the detrimental impact of the ambient humidity level on the metal-air cells. Exposed metal-air cells may absorb water from the air through the oxygen electrode and fail due to a condition called flooding, or they may release water vapor from the electrolyte through the oxygen electrode and fall due to drying. 
     Typically metal-air cells are designed to have a relatively large oxygen electrode surface, so that the largest power output possible can be obtained from a cell of a given volume and weight. Once air is introduced into a metal-air battery housing, the oxygen-bearing air is distributed to all oxygen electrode surfaces. However, in multiple cell systems it is common for an air distribution path to extend from a fan for a lengthy distance and sequentially across oxygen electrode surfaces. Oxygen may be depleted from the air stream flowing along the distribution path so that the oxygen concentration at the end of the distribution path falls below a level desired for optimal power production from all the cells. As a result of the nonuniform air flow distribution, each of the cells may operate at a different current (when the cells are arranged in parallel) and voltage (when the cells are arranged in series), which is not optimal. 
     If one uses such an air distribution path or paths with a flow through system as in Cheiky, the oxygen depletion problem may be overcome by moving a large volume of air through the battery housing so that the amount of oxygen removed from the air flow in the upstream portions of the distribution path has a negligible impact on the oxygen concentration in downstream portions of the distribution path. However, using such a large volume of fresh air may subject the battery to the flooding or drying problems described above. Pedicini at least partially resolves the flooding or drying out problems by recirculating air within the battery housing and continuously replenishing a portion of the recirculated air. Pedicini may nonetheless experience some oxygen depletion problems if using an air distribution path that extends from a fan for a lengthy distance and sequentially across oxygen electrode surfaces. 
     One drawback with the current design of metal-air cells is that the cells tend to be somewhat larger in size than conventional electrochemical power sources. This size constraint is caused, in part, by the requirements of having an anode, a cathode, an electrolyte, a cell casing of some sort, and an air manager or an air passageway of some sort to provide the reactant air to the cell. These elements all take up a certain amount of valuable space. 
     In attempting to design smaller metal-air cells and batteries, one concern is to provide a sufficient amount of air to operate the cells at their desired capability while also preventing too much air from reaching the cells during periods of non-use. A vast improvement in air manager technology is found in the above-mentioned U.S. Pat. No. 5,691,074, entitled “Diffusion Controlled Air Vent for a Metal-Air Battery” to Pedicini, which is incorporated herein by reference. Pedicini discloses, in one embodiment, a group of metal-air cells isolated from the ambient air except for an inlet and an outlet passageway. These passageways may be, for example, elongate tubes. An air-moving device positioned within the housing forces air through the inlet and outlet passageways to circulate the air across the oxygen electrodes and to refresh the circulating air with ambient air. The passageways are sized to allow sufficient airflow therethrough while the air mover is operating but also to restrict the passage of water vapor therethrough while the passageways are unsealed and the air mover is not operating. 
     When the air mover is off and the humidity level within the cell is relatively constant, only a very limited amount of air diffuses through the passageways. The water vapor within the cell protects the oxygen electrodes from exposure to oxygen. The oxygen electrodes are sufficiently isolated from the ambient air by the water vapor such that the cells have a long “shelf life” without sealing the passageways with a mechanical air door. These passageways may be referred to as “diffusion tubes”, “isolating passageways”, or “diffusion limiting passageways” due to their isolating capabilities. 
     The isolating passageways act to minimize the detrimental impact of humidity on the metal-air cells, especially while the air-moving device is off. A metal-air cell that is exposed to ambient air having a high humidity level may absorb too much water through its oxygen electrode and fail due to a condition referred to as “flooding.” Alternatively, a metal-air cell that is exposed to ambient air having a low humidity level may release too much water vapor from its electrolyte through the oxygen electrode and fail due to a condition referred to as “drying out.” The isolating passageways limit the transfer of moisture into or out of the metal-air cells while the air moving device is off, so that the negative impacts of the ambient humidity level are minimized. 
     The efficiency of the isolating passageways in terms of the transfer of air and water into and out of a metal-air cell can be described in terms of an “isolation ratio.” The “isolation ratio” is the rate of the water loss or gain by the cell while its oxygen electrodes are fully exposed to the ambient air as compared to the rate of water loss or gain by a cell while its oxygen electrodes are isolated from the ambient air except through one or more limited openings. For example, given identical metal-air cells having electrolyte solutions of approximately thirty-five percent (35%) KOH in water, an internal relative humidity of approximately fifty percent (50%), ambient air having a relative humidity of approximately ten percent (10%), and no fan-forced circulation, the water loss from a cell having an oxygen electrode fully exposed to the ambient air should be more than 100 times greater than the water loss from a cell having an oxygen electrode that is isolated from the ambient air except through one or more isolating passageways of the type described above. In this example, an isolation ratio of more than 100 to 1 should be obtained. 
     In accordance with the above-referenced example from Pedicini, the isolating passageways function to limit the amount of oxygen that can reach the oxygen electrodes when the fan is off and the internal humidity level is relatively constant. This isolation minimizes the self-discharge and leakage or drain current of the metal-air cells. Self-discharge can be characterized as a chemical reaction within a metal-air cell that does not provide a usable electric current. Self-discharge diminishes the capacity of the metal-air cell for providing a usable electric current. Self-discharge occurs, for example, when a metal-air cell dries out and the zinc anode of oxidized by the oxygen that seeps into the cell during periods of non-use. Leakage current, which is synonymous with drain current, can be characterized as the electric current that can be supplied to a closed circuit by a metal-air cell when air is not provided to the cell by an air moving device. The isolating passageways as described above may limit the drain current to an amount smaller than the output current by a factor of at least fifty (50) times. 
     In addition to humidity differentials, the isolation ratio appears to be dependent upon the pressure differential that can be induced by the fan or other type of air mover and the degree to which the isolating passageways slow the diffusion of air and water when the fan is off. In the past, air moving devices used in metal-air batteries have been bulky and expensive relative to the volume and cost of the metal-air cells. Although a key advantage of metal-air cells is their high energy density resulting from the low weight of the oxygen electrode, this advantage is compromised by the space and weight required by an effective air-moving device. Space that otherwise could be used for battery chemistry to prolong the life of the battery must be used to accommodate an air-moving device. Increasing the size and power of the fan or lengthening the isolating passageways to increase the isolation ratio, however, generally would lead one to increase the size of the cell or the battery. In other words, attempts to reduce the size of the cell or the battery have been somewhat limited by the need for an adequate isolation ratio and an adequately sized fan or air mover. This loss of space can be critical to attempts to provide a practical metal-air cell in small enclosures such as the “AA” cylindrical size now used as a standard in many electronic devices. 
     Even though numerous improvements to air managers for metal-air cells have been previously disclosed, there is always a desire for air managers that cooperate with metal-air cells in a manner that further enhances the efficiency, power and lifetime of the metal-air cells. For example, further advances in the area of evenly distributing oxygen laden air across the oxygen electrodes in a metal-air battery should further enhance the efficiency, power and lifetime of metal-air batteries. 
     There is a need, furthermore, for a metal-air cell and/or battery pack that is as small and compact as possible, that occupies less of the volume available for battery chemistry, and provides adequate power with an adequate isolation ratio. These advantages must be accomplished in a metal-air cell or battery pack that provides the traditional power and lifetime capabilities of a metal-air cell in a low cost, efficient manner. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide a removable metal-air cell pack used to power an electrical device, to protect the cell pack from negative effects of ambient air when power is not demanded from the cell pack, and to avoid the need to supply an air moving device with every cell pack. 
     The present invention accomplishes this object by providing in combination (1) a cell pack that includes one or more isolation passageways positioned to protect the metal-air cell or cells from the ambient air when no air mover is active to force air to the cell or cells, and the passageway or passageways remain unsealed, and (2) an electrical device configured to removably receive the cell pack in a manner which allows an air mover associated with the electrical device to communicate with at least one of the isolation passageways of the cell pack to provide air to the cell or cells. 
     In one embodiment of the present invention the isolation passageway is an isolating or a diffusion pathway in the form of a tube or tubes. An intake pathway and an exhaust pathway may be used or, alternatively, a single pathway may be used. 
     Generally described, the present invention provides a battery powered device, comprising a removable metal-air battery including a ventilation passageway communicating between an interior and an exterior of said battery; a docking station at which said metal-air battery may be removably mated; an air moving device exterior to said metal-air battery; and an upstream passageway communicating between said air moving device and said ventilation passageway of said metal-air battery when said metal-air battery is mated at said docking station, said ventilation passageway being sized to restrict air flow therethrough while said ventilation passageway remains unsealed and the air moving device is inoperative. 
     In a preferred embodiment, said ventilation passageway comprises a diffusion tube, and may be paired with an outlet diffusion tube depending on the nature of the air mover, which may be a fan, or a reciprocating air mover such as a diaphragm pump. The device may further comprise a perforated plate defining apertures positioned to receive and uniformly distribute air flow from said inlet diffusion tube to one or more air electrodes within said metal-air battery. 
     The diffusion tubes preferably have a length to width ratio of at least 10 to 1. In a preferred embodiment, they have a length of about 0.3 to 2.5 inches, and a width of about 0.03 to 0.3 inch. 
     According to another of its aspects, the invention provides, in combination, an air manager and a metal-air battery, said metal-air battery comprising one or more metal-air cells and a ventilation passageway communicating between an interior and an exterior of said battery; and said air manager comprising a housing comprising a docking station at which said metal-air battery may be removably mated with said housing; a air moving device positioned within said housing; and an upstream passageway connecting said air moving device to an opening positioned so as to communicate with said ventilation passageway of said metal-air battery when said metal-air battery is mated at said battery port; said ventilation passageway being sized to restrict air flow therethrough while said passageway remains unsealed and the air moving device is inoperative. 
     According to another of its aspects, the invention provides electronic device powered by a metal-air battery including an input diffusion tube, comprising a battery port at which said metal-air battery may be removably mated with said electronic device; an air moving device positioned within said electronic device; and a passageway connecting said air moving device to an outlet positioned so as to communicate with said input diffusion tube of said metal-air battery when said metal-air battery is mated at said battery port, being sized to restrict air flow therethrough while said passageway remains unsealed and the air moving device is inoperative. 
     A further embodiment includes an electronic device driven by a metal-air battery with an input diffusion tube. The electronic device has an exterior surface and a battery port for mating with the metal-air battery. The device also has an intake diffusion tube positioned within the device so as to communicate between the exterior and the input diffusion tube of the metal-air battery when the metal-air battery is positioned within or adjacent to the battery port. A fan is positioned within the intake diffusion tube of the electronic device. This embodiment results in a replaceable metal-air battery for mating with an electrical device with an internal fan for providing reactant air. 
     The present invention provides a metal-air power supply having at least one metal-air cell. The power supply also has at least one passageway capable of passing sufficient air to operate the cell when operatively associated with an operating air moving device. The passageway is further operative, while unsealed and not under the influence of the operating air movement device, to restrict airflow through the passageway. The air movement device itself is separable from the power supply. 
     A further embodiment of the present invention provides a two-part metal-air cell. The cell has an air manager cap with an air manager pathway positioned within the cap. The air manager pathway has an air inlet and a cap mating connector. An air movement device is positioned to cause a flow of air within the air manager pathway. The cell housing also has a chemistry body that is detachable from the air manager cap. The chemistry body has a chemistry body diffusion pathway with a body mating connector. The cap mating connector and the body mating connector are sized to mate with each other when the cap and chemistry body are brought into engagement. The air movement device may be capable of reciprocating motion. 
     The invention, also provides a metal-air battery having a distributor for approximately uniformly distributing oxygen-laden air to multiple oxygen electrodes, which may be associated with one or more metal-air cells, in response to operation of an air moving device. As a result of the distribution of oxygen, each of the metal-air cells operate at approximately the same current (when the cells are arranged in parallel) and voltage (when the cells are arranged in series) so that the battery provides an optimum amount of electrical power over an extended period of time. 
     Preferably the distributor is further operative, or associated with one or more restrictive passageways that are operative, while unsealed to provide a barrier function that protects the metal-air cells from the ambient environment at the appropriate time, such as while the air moving device is not operating. That is, while the air moving device is off, or not providing air to the metal-air battery, the distributor and/or restrictive passageway or passageways restrict air flow to the oxygen electrodes so that the metal-air battery is capable of having a long shelf life without requiring), a door or doors, or the like, to seal the oxygen electrodes from the ambient environment. 
     In accordance with one aspect of the invention, a ventilation system is provided for supplying air to a metal-air cell assembly having at least a first oxygen electrode and a second oxygen electrode. The ventilation system has a housing that defines a chamber for receiving the metal-air cell assembly. The ventilation system further includes an air moving device for moving air through a reactant air flow path to the chamber. The ventilation system further includes a perforated member that is positioned in the reactant air flow path for distributing air flow approximately uniformly through the chamber in response to operation of the air moving device. The perforated member may also restrict air flow to the chamber while the air moving device is not providing air to the metal-air battery and the reactant air flow path is unsealed, or alternatively another component defines a restriction in the reactant air flow path that restricts air flow to the chamber while the air moving device is not providing air to the metal-air battery and the reactant air flow path is unsealed. 
     In another aspect of the present invention, a metal-air power supply is provided. The metal-air power supply includes a first plenum communicating with a first oxygen electrode and a second plenum communicating with a second oxygen electrode. The metal-air power supply further includes a perforated member that is positioned within the reactant air flow path for distributing air flow approximately uniformly between the plenums in response to operation of an air moving device. The perforated member may also restrict air flow to the plenums while the air moving device is off and the reactant air flow path is unsealed, or alternatively another component defines a restriction in the reactant air flow path and restricts air flow to the plenums while the air moving device is not providing air to the metal-air power supply and the reactant air flow path is unsealed. 
     In another aspect of the invention, the metal-air power supply may be docked to an electronic device that is powered by the metal-air power supply. The electronic device may at least partially define the reactant air flow path, and may include the air moving device and the restriction in the reactant air flow path that restricts air flow to the plenums while the air moving device is off and the air flow path is unsealed. 
     The air moving device may sweep a continuous flow of fresh air from the ambient environment across the oxygen electrodes at a flow rate sufficient to achieve the desired power output. Alternatively, the air moving device may recirculate air across the oxygen electrodes, and the air moving device may further move air through one or more passageways to refresh the recirculating air. 
     Regarding the perforated members in greater detail, each preferably defines a plurality of apertures that at least partially define the reactant air flow path, and each aperture defines a width perpendicular to the direction of flow therethrough and a length in the direction of flow therethrough, the length being, one or multiple times greater than the width. The perforated member may be a plate, or it may be an elongate ventilation passageway, such as a tube, having the apertures distributed along its length. A first of the apertures is more proximate to a first plenum than a second plenum and a second of the apertures is more proximate to the second plenum than the first plenum. Alternatively the perforated member may be in the form of a bundle of tubes; an aggregate of materials that define air paths therebetween, such as a bundle of fibers with air paths defined between the fibers; a piece or porous material that is preferably thick; or the like. 
     In another aspect of the invention, the aforementioned oxygen electrodes are part of a stack of metal-air cells. The metal-air cells may have spaced protrusions, and the air moving device may be mounted between protrusions of the cells. Further, each metal air cell includes a case. Each case may include a pair of unitary case portions, each of which has side walls extending from a panel in a common direction to define a cavity. For each cell, a first case portion is mounted to a second case portion such that the side walls of the first case portion extend into the cavity of the second case portion. 
    
    
     Other objects, features and advantages of the present invention will become apparent upon reviewing the following description of exemplary embodiments of the invention, when taken in conjunction with the drawings and the amended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a metal-air battery exploded away from an electronic device that is powered by the metal-air battery, in accordance with a first exemplary embodiment of the present invention. 
     FIG. 2 is a diagrammatic side cross-sectional view of the metal-air battery of FIG. 1, taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is a diagrammatic rear cross-sectional view of the metal-air battery of FIG. 1, taken along line  3 — 3  of FIG.  1 . 
     FIG. 4 is an isolated cross-sectional view of a distributor plate of the metal air battery of FIG. 1, taken along line  4 — 4  of FIG.  3 . 
     FIG. 5 is a partially cut-away, diagrammatic front cross-sectional view of the metal-air battery of FIG. 1, taken along line  5 — 5  of FIG.  1 . 
     FIG. 6 is a top plan view of a fan frame mounted to a stack of cells of the metal-air battery of FIG.  1 . 
     FIG. 7 is an isolated exploded view of a cell case of a metal-air cell of the battery of FIG.  1 . 
     FIG. 8 is a diagrammatic view of a metal-air cell of the battery of FIG.  1 . 
     FIG. 9 is a side cross-sectional view of a metal-air battery in accordance with a second exemplary embodiment of the present invention. 
     FIG. 10 is an isolated view of an air distributor tube of the metal-air battery of FIG.  9 . 
     FIG. 11 is a cross-sectional view of the air distributor tube of FIG. 10, taken along line  11 — 11 . 
     FIG. 12 is a diagrammatic view of a metal-air battery exploded away from an electronic device that is powered by the metal-air battery, in accordance with a third exemplary embodiment of the present invention. 
     FIG. 13 is a diagrammatic cross-sectional view of the electronic device of FIG. 12, taken along line  13 — 13 . 
     FIG. 14 is a diagrammatic side cross-sectional view of the metal-air battery of FIG. 12, taken along line  14 — 14 . 
     FIG. 15 is a diagrammatic side cross-sectional view of a metal-air battery in accordance with a fourth exemplary embodiment of the present invention. 
     FIG. 16 is a diagrammatic cross-sectional view of the metal-air battery of FIG. 15 taken along line  16 — 16 . 
     FIG. 17 is a cross-sectional view of an electronic device with a diffusion tube and an internal fan mated with a metal-air battery with intake and exhaust diffusion tubes. 
     FIG. 18 is a cross-sectional view of an “AA” size metal-air battery with an air manager cap having a diffusion tube with an internal fan. 
     FIG. 19 is a cross-sectional view of a diffusion tube with an internal fan. 
     FIG. 20 is a cross-sectional view of the diffusion tube with an internal fan taken along line  20 — 20  of FIG.  19 . 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring now in more detail to the drawings, in which like numerals refer to like parts throughout the several figures, FIG. 1 diagrammatically illustrates a metal-air battery  20  exploded away from an electronic device  22  that receives and is powered by the metal-air battery. The metal-air battery  20  includes a battery housing  24  through which a reactant air flow path is defined. As will be discussed in greater detail below, air is moved along the reactant air flow path by an air moving device, such as a fan  70  (FIG.  5 ), to supply air to metal-air cells  60   a-f  (FIG. 2) within the battery housing  24 . An inlet ventilation passageway  30 , which includes an inlet opening  32  defined through the battery housing  24 , functions as an air inlet portion of the reactant air flow path. An outlet ventilation passageway  34 , which includes an outlet opening  36  defined through the battery housing  24 , functions as an outlet portion of the reactant air flow path. 
     The reactant air flow path can be best visualized with reference also to FIG. 2, which is a diagrammatic side cross-sectional view of the metal-air battery  20  taken along line  2 — 2  of FIG.  1 . The reactant air flow path of the metal-air battery  20  originates from the ambient environment external to the electronic device  22  and the metal-air battery. The reactant air flow path then extends through the inlet ventilation passageway  30 , which  30  further includes an air inlet tube  56  that is contiguous with the inlet opening  32  (shown in dashed lines) of the inlet ventilation passageway. The reactant air flow path then extends through a battery chamber  54  defined within the battery housing  24 . The reactant air flow path extends between the metal-air cells  60   a-f  within the chamber  54 . Lastly, the reactant air flow path extends through the outlet ventilation passageway  34 , which further includes an air outlet tube  58  that is contiguous with the outlet opening  36  (shown in dashed lines) of the outlet ventilation passageway. 
     A perforated member in the form of a perforated distributor plate  66  is disposed within the battery chamber  54  and at least partially defines the reactant air flow path. Alternatively the perforated member may be in the form of a bundle of tubes; an aggregate of materials that define air paths therebetween, such as a bundle of fibers with air zinc paths defined between the fibers; a piece or porous material that is preferably thick; or the like. 
     The distributor plate  66  functions to distribute air flowing along the reactant air flow path so that air flow, and therefore oxygen, is evenly distributed between the metal-air cells  60   a-f  contained within the battery chamber  54 . The oxygen is a reactant in the electrochemical reactions of the metal-air cells  60   a-f , and the even distribution of oxygen causes the battery  20  to optimally provide power to the electronic device  22 , as  10  discussed in greater detail below. Air is moved through the reactant air flow path in response to operation of the fan  70  (FIG.  5 ), which is hidden from view in FIG.  2 . 
     Referring back to FIG. 1, the electronic device  22  may be a conventional portable computer, camcorder, or any other type of electronic device  22  capable of being powered by one or more metal-air cells. The electronic device  22  includes a device case  38  having a conventional docking station  40  for receiving the metal-air battery  20 . More particularly, the docking station  40  defines a conventional docking cavity  42  for receiving the metal-air battery  20 . Those skilled in the art will appreciate that the metal-air battery  20  can be coupled to a variety of differently configured docking stations. For example, a docking station can be flush with an external surface of the device case  38  such that the docking station does not include a docking cavity  42 . 
     The metal-air battery  20  can be repeatedly installed to and removed from the docking station  40  of the electronic device  22 . For example, the metal-air battery  20  may be rechargeable, in which case the metal-air battery may be removed from the docking station  40  for recharging purposes, and then be recoupled to the docking station after being  25  recharged. Alternatively, the metal-air battery  20  may be a disposable, primary battery, such that periodically a spent metal-air battery coupled to the docking station  40  is replaced with a fresh metal-air battery. 
     The docking cavity  42  is defined by an inner wall and four walls that extend outward from the peripheral edges of the inner wall. The docking station  40  includes two conventional electrical contacts  44  and four conventional male locking devices  46  that are all associated with the inner- wall of the docking cavity  42 . Three of the male locking devices  46  are hidden from view in FIG. 1. A separate male locking device  46  is preferably positioned at each comer of the inner wall of the docking cavity  42 , and the male locking devices securely and releasably couple the metal-air battery  20  to the electronic device  22 . 
     As illustrated in FIG. 2, the battery housing  24  is formed by joining a tray  26  and a cover  28 . The air openings  32  and  36  (FIG. 1) are defined through the cover  28 . The battery tray  26  includes four conventional female locking devices  50 , a separate one of which is proximate to each of the four comers of the bottom wall of the battery tray. Two of the female locking devices are hidden from view in FIG.  2 . The female locking devices  50  are operative for releasably interlocking with the male locking devices  46  (FIG. 1) of the docking station  40  (FIG.  1 ). The battery tray  26  further includes a pair of electrical contacts  48  that electrically communicate with the electrical contacts  44  (FIG. 1) of the electronic  5  device  22  (FIG. 1) while the female locking devices  50  are interlocked with the male locking devices  46 . 
     A lip  52  extends around the upper periphery of the battery tray  26  and is in receipt of the bottom edges of the battery cover  28 . The battery tray  26  and the battery cover  28  are preferably molded of acrylonitrile butadiene styrene (ABS) or another non-conductive plastic. The seam of the battery housing  24 , which is defined where the bottom edges of the battery cover  28  fit into the lip  52 , is preferably sealed by solvent bonding. 
     As mentioned above, the inlet ventilation passageway  30  includes the inlet opening  32  (FIG. 1) and the inlet tube  56 , and the outlet ventilation passageway  34  includes the outlet opening  36  (FIG. 1) and the outlet tube  58 . The inlet tube  56  is mounted to the battery cover  28  such that the upstream end of the inlet tube is contiguous with and open to the inlet opening  32 . Similarly, the outlet tube  58  is mounted to the battery cover  28  such that the downstream end of the outlet tube is contiguous with and open to the outlet opening  36 . The ventilation passageways  30  and  34  preferably provide the only communication paths between the battery chamber  54  and the environment external to the battery housing  24 . Air entering the inlet opening  32  passes into the battery chamber  54  solely by way of the downstream end of the inlet tube  56 . Similarly, air within the battery chamber  54  enters the outlet ventilation passageway  34  solely by way of the upstream end of the outlet tube  58 . 
     The ventilation passageways  30  and  34  are preferably constructed to allow a sufficient amount of air to flow through the reactant air flow path while the fan  70  (FIG. 5) is operating, so that a large a power output, typically at least 20 mA per square cm of air electrode, can be obtained from the metal-air cells  60   a-f . Further, the ventilation passageways  30  and  34  are preferably constructed to provide a barrier function while the fan  70  is not operating. Regarding the barrier function in greater detail, the ventilation  30  passageways  30  and  34  function so that air flow through the reactant air flow path is restricted while the fan  70  is not operating. As a result, a minimal amount of oxygen moves into the battery chamber  54  while the fan  70  is not operating. Further, the ventilation passageways  30  and  34 , and the entire reactant air flow path, remain unsealed while the fan  70  is off or otherwise not supplying air to the metal-air battery  20 . That is, the reactant air flow path continues to define a passageway from the ambient environment to the metal-air cells  60   a-f  while the fan  70  is off or otherwise not supplying air to the metal air battery. For example the reactant air flow path is not closed by air doors or the like. That is, the ventilation passageways  30  and  34  are operative, while the fan  70  is not supplying air to the metal-air battery  20 , for restricting air flow to the metal-air cells  60   a-f  so that the metal-air battery  20  experiences rrunimal self discharge and is capable of having a long shelf life without requiring a door or doors to seal the ventilation passageways. The barrier function of the ventilation passageways  30  and  34  is preferably the result of the sizing of the ventilation passageways, as will be discussed in greater detail below. 
     Each of the metal-air cells  60   a-f  includes a cell case  86  (FIG. 7) having a closed wall  59  (FIG. 7) and a mask wall  61  (FIGS.  7 - 8 ). Oxygen that is a reactant in the electrochemical reaction of the metal-air cells  60   a-f  is received through the mask walls  61  while the fan  70  (FIG. 5) is operating. As shown in FIG. 2, the metal-air cells  60   a-f  are arranged in a stack, and each of the mask walls  61  faces one of the plenums  64   a ,  64   b  or  64   c  defined between the metal-air cells within the battery chamber  54 . The closed walls  59  of the metal-air cells are isolated from the plenums  64   a-c . In contrast, the mask walls  61  of adjacent metal-air cells are spaced apart and define the plenums  64   a-c . That is, the mask walls  61  of the metal-air cells  60   a  and  60   b  face and at least partially define the plenum  64   a ,  15  the mask walls  61  of the metal-air cells  60   c  and  60   d  face and at least partially define the plenum  64   b , and the mask walls  61  of the metal-air cells  60   e  and  60   f  face and at least partially define the plenum  64   c.    
     The necessary spacing between the metal-air cells  60   a-f , which defines the plenums  64   a-c , can be established through the use of spacers  62 , only several of which are illustrated in the figures. Any conventional spacers can be used to at least partially provide the plenums  64   a-c . Further, the side edges of the metal-air cells  60   a-f  abut opposite side walls of the battery housing  24  to isolate the plenums  64  from one another. 
     The distributor plate  66  is mounted across and abuts the downstream ends of the metal-air cells  60   a-f . Thus, the distributor plate  66  partially bounds each of the plenums  64   a-c  and separates the battery chamber  54  into an upstream portion and a downstream portion. The distributor plate  66  separates the upstream and downstream portions of the battery chamber  54  so that air moving from the upstream portion to the downstream portion of the battery chamber must pass through perforations, or apertures  72  (FIGS.  3  and  4 ), defined through the distributor plate  66 . More specifically, the reactant air flow path is divided into branches, and the branches of the reactant air flow path extend through the apertures  72 . Alternatively the distributor plate  66  is mounted across and abuts the upstream ends of the metal-air cells  60   a-f.    
     As will be discussed in greater detail below, a fan control circuit that-includes a circuit board  68  is preferably utilized to facilitate operation of an air moving device, such as the fan  70  (FIG.  5 ), to cause air to flow along the reactant air flow path to supply air to metal-air cells  60   a-f . More specifically, in response to operation of the fan  70 , air flows from the ambient environment into the inlet opening  32  (FIG.  1 ), through the inlet tube  56 , through the fan  70 , through the plenums  64   a-c , through the apertures  72  (FIGS. 3 and 4) of the distributor plate  66 , through the outlet tube  58 , and then through the outlet opening  36  back to the ambient environment. 
     FIG. 3 is a diagrammatic cross-sectional view of the metal-air battery  20  taken along line  3 — 3  of FIG.  1 . The peripheral edges of the distributor plate  66  preferably extend to and engage interior surfaces of the battery housing  24  so that the multiple apertures  72  that extend through the distributor plate  68  are the only passages communicating between the upstream and the downstream portions of the battery chamber  54 . The apertures are sized and arranged so that air flowing through the reactant air flow path is evenly distributed so that the oxygen concentrations at each of the mask walls  61  (FIGS. 7-8) of the metal-air cells  60   a-f  (FIG. 2) are approximately identical while the fan  70  (FIG. 5) is operating. 
     The plenums  64   a-c  (FIG. 2) are primarily hidden from view in FIG. 3, but the positions of the plenums  64  are illustrated by broken lines in FIG.  3 . An upper row of apertures  72  of the distributor plate  66  is aligned with and communicates with the plenum  64   a , a middle row of apertures is aligned with and communicates with the plenum  64   b , and a lower row of apertures is aligned with and communicates with the plenum  64   c . Uniform air flow distribution is preferably achieved by virtue of each of the apertures  72  being nearly identically sized and each of the plenums  64   a-c  being associated with an identical number of apertures. The uniform air flow distribution causes each of the metal-air cells  60   a-f  to operate at approximately the same current (when the cells are arranged in parallel) and voltage (when the cells are arranged in series). 
     FIG. 4 is an isolated cross-sectional view of the distributor plate  66  taken along line  4 — 4  of FIG.  3 . The aperture  72  illustrated in FIG. 4 is representative of all of the other apertures of the distributor plate  66 . As illustrated in FIG. 4, each aperture  72  has a length “L 1 ” measured in the direction of flow therethrough, and a width “W 1 ” measured perpendicular to the direction of flow therethrough. The length “L 1 ” is preferably greater than the width “W 1 ” such that the apertures  72  sufficiently restrict flow to provide the uniform air flow distribution. The sizing of the apertures  72  will be discussed in greater detail below. 
     As mentioned above with reference to FIG.  2  and the first exemplary embodiment of the invention, each of the ventilation passageways  30  and  34  provide a barrier function such that air flow therethrough is restricted while the fan  70  (FIG. 5) is not operating and the ventilation passageways are unsealed. In accordance with an alternative embodiment of the present invention, the outlet ventilation passageway  34  may be large such that the outlet ventilation passageway does not provide the barrier function while the fan  70  is not supplying air to the metal-air battery  20 , in which case the distributor plate  66  may be characterized as defining the downstream end of the battery housing  24 . In this alternative embodiment, the distributor plate  66  further performs the barrier function in addition to the flow distribution function. 
     In both the first exemplary embodiment and the alternative embodiment, the apertures  72  in the distributor plate  66  are constructed to allow a sufficient amount of air to flow through the reactant air flow path while the fan  70  (FIG. 5) is operating so that a large power output can be obtained from the metal-air cells  60   a-f . In the alternative embodiment, the apertures  72  also function so that air flow through the reactant air flow path is restricted, so that a minimal amount of oxygen moves into the battery chamber  54  (FIG. 2) while the fan  70  is not operating and the reactant air flow path is unsealed. More specifically, apertures  72  remain unsealed while the fan  70  is off or otherwise not supplying air to the metal-air battery  20 . That is, the reactant air flow path continues to define a passageway to the metal-air cells  60   a-f  while the fan is off or otherwise not supplying air to the metal-air battery. For example the reactant air flow path is not closed by air doors or the like. Thus, the apertures  72  in the distributor plate  66  are operative, while the fan  70  is not supplying air to the metal-air battery  20 , for restricting air flow to the metal-air cells  60   a-f  so that the metal-air battery is capable of having a long shelf life without requiring a door or doors to seal the apertures  72 . The barrier function of the apertures  72  is preferably the result of the sizing of the apertures. More particularly, each of the apertures  72  preferably has a length and width selected to substantially eliminate air flow therethrough while the fan  70  is not supplying air to the metal-air battery  20 . The sizing of the apertures  72  in the distributor plate  66  is discussed in greater detail below. 
     FIG. 5 is a diagrammatic end cross-sectional view of the metal-air battery  20  taken along a line  5 — 5  of FIG.  1 . The fan  70  includes a motor  82  that rotates an impeller  84 . The fan  70  is part of a fan assembly  77  that further includes a rectangular fan frame  78  and  25  braces  80  that span between the fan frame and the motor  82 . The fan assembly  77  further includes a shroud  85  that is partially cut away in FIG. 5 so that numerous components of the metal-air battery  20  are seen. The shroud  85  extends inward from each side of the fan frame  78  and defines a central circular opening through which air is drawn in response to rotation of the impeller  84 . Other types of air moving devices may be used in place of the fan assembly  77 . 
     Each of the metal-air cells  60   a-f  includes a pair of protrusions  74  between which a recess  76  (FIGS. 7-8) is defined. The fan assembly  77  fits securely into the recesses  76  of the metal-air cells  60   a-f . As mentioned previously, the metal-air cells  60   a-f  are arranged in a stack, and the recesses  76  are defined at the upstream end of the stack such that the fan assembly  77  is mounted into the upstream end of the stack. This nested arrangement is illustrated in FIG. 6, which is an isolated top plan view of the stack of metal air cells  60   a-f  with the fan assembly  77  nested between the protrusions  74 . FIG. 6 is also  12  representative of an isolated bottom plan view of the stack of metal air cells  60   a-f  with the fan assembly  77  nested between the protrusions  74 . 
     FIG. 7 is an isolated exploded view of a cell case  86  of one of the metal-air cells  60   a-f . The cell case  86  includes a tray  88  that includes side walls extending upward from the periphery of the closed wall  59  to define a tray cavity. The tray  88  defines the two protrusions  74 , and each protrusion defines a protrusion cavity  90 , which will be discussed in greater detail below. Each cell case  86  further includes a cover  92  that includes the mask wall  61 , which defines a plurality of apertures  96  therethrough. The cover  92  includes walls that extend downward from the periphery of the mask wall  61 . 
     The cover  92  is installed to the tray  88  by moving the ends of the walls of the cover  92  that are opposite from the mask wall  61  into the tray cavity defined by the tray  88 . This movement is continued until the edges of the walls of the cover  92  that are opposite from the mask wall  61  abut the closed wall  59  of the tray  88 . As a result, the tray cavity is enclosed. 
     Each metal-air cell  60  includes an oxygen electrode (not shown) and an anode (not shown) that are enclosed within the tray cavity. The anode is proximate to the closed wall  59  and the oxygen electrode is proximate to the mask wall  61  and receives oxygen through the apertures  96 . The openings, or apertures  96 , are preferably about 0.055 inch in diameter and together preferably provide an pen area of about 4 percent of the area of the oxygen electrode. An open area in a range from about 1 percent to about 5 percent of the oxygen electrode area is suitable. 
     FIG. 8 is a diagrammatic isolated view of one of the metal-air cells  60   a-f , each of which is identical. FIG. 8 is diagrammatic because the apertures  96  (FIG. 7) of the mask wall  61  are not illustrated. External ends of electrode tabs or terminals  98  extend through the protrusion cavities  90  (FIG.  7 ), and the protrusion cavities are filled with potting, such as epoxy, to hold and provide leak-tight seals around the terminals  98 . Internal ends of the terminals  98  are electrically connected, respectively, to the oxygen electrode and anode within the cell case  86 . The external ends of the terminals  98  of the several metal-air cells  60   a-f  are electrically connected, in a manner known to those skilled in  30  the art, to the electrical contacts  48  (FIGS. 2-3 and  5 ) of the metal-air battery  20  (FIGS. 1-3 and  5 ) so that the electrical contacts  48  can electrically communicate with the electrical contacts  44  (FIG. 1) of the electronic device  22  (FIG. 1) to power the electronic device in response to operation of the fan  70  (FIG.  5 ). 
     The tray  88  and the cover  92  are preferably molded of acrylonitrile butadiene  35  styrene (ABS) or another non-conductive plastic. Each of the tray  88  and the cover  92  are unitary, meaning that each is molded from a single piece of material and does not include separate but joinable parts. When the tray  88  and the cover  92  are assembled as illustrated in FIG. 8, the seam between the tray and the cover is preferably sealed by solvent bonding. The oxygen electrode, anode and other internal components of the metal-air cells  60   a-f  may be as described in U.S. Pat. No. 5,506,067 or U.S. Provisional Patent Application No. 60/063,155, both of which are incorporated herein by reference. 
     Alternatively, each of the metal-air cells within the battery housing  24  may be of the type having an anode positioned between a pair of oxygen electrodes. Such dual oxygen electrode metal-air cells are disclosed in U.S. Pat. No. 5,569,551 and U.S. Pat. No. 5,639,568, both of which are incorporated herein by reference. For example, and referring to FIG. 2, a single of such dual oxygen electrode cells can be used in place of the metal-air cells  60   b  and  60   c  such that one of the oxygen electrodes of the metal-air dual oxygen electrode cell receives oxygen from the plenum  64   a  and the other of the oxygen electrodes of the dual oxygen electrode cell receives oxygen from the plenum  64   b.    
     Referring again to FIG. 2, the sizing of the ventilation passageways  30  and  34  will be discussed in detail. Each of the ventilation passageways  30  and  34  preferably has a width that is generally perpendicular to the flow path therethrough, and a length that is generally parallel to the flow path therethrough. The length and the width are selected to substantially eliminate air flow into the housing  24  when the fan  70  (FIG. 5) is not supplying air to the metal-air battery  20 . The length is greater than the width, and more preferably the length is greater than about twice the width. The use of larger ratios between length and width of the ventilation passageways  30  and  34  is preferred, and depending upon the nature of the battery  20  (FIGS. 1-3 and  5 ) the ratio can be more than 200 to 1. However, the preferred ratio of length to width is about 10 to 1. 
     It is preferable for the inlet tube  56  and the outlet tube  58  to provide the above-mentioned desired length-to-width ratios of the ventilation passageways  30  and  34 . That is, the tubes  56  and  58  each have a cross sectional area and length selected to substantially eliminate air flow into the housing  24  when the fan  70  is not supplying air to the metal-air battery  20 . The tubes  56  and  58  each may have a length of about 0.3 to 2.5 inches, with about 0.88 to 1.0 inches preferred, and a width of about 0.03 to 0.3 inches, with about 0.09 to 0.19 inches preferred. The total open area of each tube, measured perpendicular to the flow path therethrough, is therefore about 0.0007 to 0.5 square inches. 
     The preferred total open area of the ventilation passageways  30  and  34  depends upon the desired capacity of the battery  20 . Any number of ventilation passageways can be used such that the aggregate open area of all of the ventilation passageways equals this preferred total open area, with each such ventilation passageway having the same or similar ratios of length to width to provide the barrier functions. Those skilled in the art will appreciate that the length of the ventilation passageways  30  and  34  may be increased, and/or the diameter decreased, if the differential pressure created by the fan  70  is increased. A balance between the differential pressure. created by the fan  70  and the dimensions of the ventilation passageways  30  and  34  can be found at which air flow into the housing  24  will be sufficiently reduced when the fan is not supplying air to the metal-air battery  20 . Although the use of circular ventilation passageways is disclosed, any conventional shape having the required ratios may be employed. Further, the ventilation passageways may be straight or curved in length. 
     Referring again to FIGS. 3-4, the sizing of the apertures  72  will be discussed in greater detail. For each aperture  72  the length “L 1 ” is preferably greater than the width “W 1 ,” and more preferably the length is greater than about twice the width. More specifically, the use of larger ratios between length and width of the apertures  72  may be preferred, especially when the outlet ventilation passageway  34  (FIG. 2) is large such that the outlet ventilation passageway does not restrict air flow therethrough while the fan  70  (FIG. 5) is not supplying air to the metal-air battery  20 . The distributor plate  66  provides the barrier function and can be characterized as defining the downstream end of the battery housing  24 , when the outlet ventilation passageway  34  does not provide the barrier function as discussed above. 
     Depending upon the nature of the battery  20  (FIGS. 1-3 and  5 ) the length to width ratio of the apertures  72  can be more than 10 to 1. However, the preferred ratio of length to width is about 2 to 1. The apertures  72  each may have a length of about 0.02 to 0.2 inches, with about 0.04 to 0.08 inches preferred, and a width of about 0.01 to 0.1 inches, with about 0.03 to 0.06 inches preferred. The total open area of each aperture  72 , measured perpendicular to the flow path therethrough, is therefore about 0.00008 to 0.008 square inches. 
     The preferred total open area of the apertures  72  depends upon the desired capacity of the battery. Any number of apertures  72  can be used such that aggregate open area of all of the apertures  72  equals this preferred total open area, with each such aperture preferably having the same or similar ratios of length to width to provide the desired flow distribution function and optionally the barrier function. Those skilled in the art will appreciate that the length of the apertures  72  may be increased, and/or the width decreased, if the differential pressure created by the fan  70  is increased. A balance between the differential pressure created by the fan  70  and the dimensions of the apertures  72  can be found at which the desired flow distribution and barrier functions are achieved. Although the use of circular apertures  72  is disclosed, any conventional shape having the required ratios may be employed. Further, the apertures  72  may be straight or curved in length. 
     Referring again to FIGS. 2 and 5, the operation of the fan  70  will be discussed in greater detail. As indicated previously, the metal-air cells  60   a-f  operate in response to operation of the fan  70  and the operation of the fan  70  is controlled by the fan control circuit which includes the circuit board  68 . The fan  70  is powered by the metal-air cells  60   a-f , and the circuit board  68  contains electronics for operating the fan  70  in response to the voltage of the cells  60 . The control circuit preferably includes a voltage sensor (not  15  shown) that monitors the voltage of the cells  60 . The voltage sensor cooperates with the circuit board  68  to operate the fan  70  when the voltage of the metal-air cells  60   a-f  reaches predetermined levels. The fan control circuit turns the fan  70  on when the voltage across the metal-air cells  60   a-f  is less than or equal to a predetermined voltage. Likewise, the fan control circuit turns the fan  70  off when the voltage across the metal-air cells  60   a-f  is, greater than or equal to a second predetermined voltage. 
     The metal-air battery  20  shown in FIGS. 1-3 and  5  may be configured to be a six volt metal-air battery with six metal-air cells. Such a battery has an energy load rating of about 70 watt/hours at a drain rate of about 6 watts and about 80 watt/hours at a drain rate of about 3 watts. The predetermined voltage for turning the fan  70  on is approximately 1.05 volts per cell, while the second predetermined voltage for turning the fan  70  off is approximately 1.10 volts per cell. The voltage monitor turns the fan  70  on when the voltage is less than or equal to approximately 1.05 volts per cell. Likewise, the voltage monitor turns the fan  70  off when the voltage is greater than or equal to approximately 1.10 volts per cell. 
     The voltage monitor determines the voltage across the oxygen electrode and anode electrode terminals  98  (FIG. 8) of the cells  60 . Because the zinc potential within the oxygen electrode of each cell is relatively stable, the oxygen electrode is used to sense the residual oxygen in the cell. As the oxygen within the housing is depleted, the voltage across each oxygen electrode diminishes. Likewise, as the flow of oxygen into the housing increases, the voltage across the oxygen electrode increases. 
     The voltage monitor can be positioned at any convenient location within or adjacent to the battery housing  24  (FIGS. 1-3 and  5 ). The preferred voltage monitor is a programmable voltage detection or sensing device, such as that sold by Maxim Integrated Products under the mark MAX8211 and MAX8212. Depending upon the desired operation of the fan  70 , the voltage monitor can be an analog circuit for a simple “on/off” switch or can incorporate a microprocessor (not shown) for a more complex algorithm. 
     FIG. 9 is a side cross-sectional view of a metal-air battery  220  in accordance with a second exemplary embodiment of the present invention. The metal-air battery  220  is  30  constructed and functions identically to the first exemplary metal-air battery  20  of FIGS. 1-3 and  5 , except for noted variations and variations that will be apparent from the following description. The metal-air battery  220  does not include the distributor plate  66  of FIGS. 2-5, and the tubes  56  and  58  of FIG. 2 have been replaced with perforated members in the form of a perforated inlet distributor tube  102 a and a perforated outlet distributor tube  102   b ,  35  respectively. Alternatively only the tube  56  is replaced with the tube  102   a , or only the tube  58  is replace with the tube  102   b.    
     The distributor tubes  102   a  and  102   b  are identical to the tubes  56  and  58 , except that each distributor tube  102   a  and  102   b  further functions to distribute air flowing  16  along the reactant air flow path so that air flow, and therefore oxygen, is evenly distributed between the metal-air cells  60   a-f  contained within the battery chamber  54 , as will be discussed in greater detail below. More specifically, the distributor tubes  102   a  and  102   b  are identical to the tubes  56  and  58 , except that each distributor tube  102   a  and  102   b  defines perforations, or apertures  104 , that are evenly spaced along its length and includes a plug  106  closing one of its ends, and the distributor tubes  102   a  and  102   b  may be longer than the tubes  56  and  58  so that the apertures  104  are uniformly arranged with respect to the metal air cells  60   a-f.    
     As illustrated in FIG. 9, the apertures  104  are nearly identically sized and approximately uniformly spaced along the length of the distributor tubes  102   a  and  102   b . However, it may be desirable to have more or larger apertures  104  toward the plugged ends of the distributor tubes  102   a  and  102   b  in order to cause a uniform flow distribution through the battery chamber  54 . Those skilled in the art will appreciate that the required sizing and arrangement of the apertures  104  along the length of the distributor tubes  102   a  and  102   b , as well as the shape of the distributor tubes, will vary depending upon the differential pressure created by the fan  70  and the sizing and arrangement of the components of the present invention. Also, the ends of the distributor tubes  102   a  and  102   b  may be sealed by solvent bonding, may be closed by collapsing, or may be sealed by other means. 
     The reactant air flow path of the metal-air battery  220  originates from he ambient environment external to the electronic device  22  and the battery. The reactant air flow path then extends through the inlet ventilation passageway  230 , which includes the inlet air distributor tube  102   a  and the inlet opening  32  (FIG.  1 ). The reactant air flow path enters the inlet air distributor tube  102   a  by way of the inlet opening  32  and exits the air distributor tube  102   a  by way of the apertures  104  of the air distributor tube  102   a . The  25  reactant air flow path further extends through the battery chamber  54  defined within the battery housing  24 . Lastly, the reactant air flow path extends through the outlet ventilation passageway  34 , which includes the outlet air distributor tube  102   b  and the outlet opening  36  (FIG.  1 ). The reactant air flow path enters the air distributor tube  102   b  by way of the apertures  104  of the air distributor tube  102   b  and exits the air distributor tube  102   b  by way of the outlet opening  36 . 
     In accordance with the second exemplary embodiment of the present invention, the volumetric flow rate through each of the apertures  104  is about equal while the fan  70  (FIG. 5) is operating. Thus, the distributor tubes  102   a  and  102   b  function to distribute air flowing along the reactant air flow path so that air flow, and therefore oxygen, is evenly distributed between the metal-air cells  60   a-f  contained within the battery chamber  54 . The oxygen is a reactant in the electrochemical reactions of the metal-air cells  60   a-f , and the even distribution of oxygen causes the battery  220  to optimally provide power to the electronic device  22 . Air is moved through the reactant air flow path in response to operation of the fan  70  (FIG.  5 ), which is hidden from view in FIG.  9 . 
     The distributor tubes  102   a  and  102   b  are identical, and FIG. 10 illustrates one of the distributor tubes. The distributor tube  102  includes a mounted end  108  that is mounted to the battery housing  24  and contiguous with the opening  32  or  36  (FIG.  1 ). The apertures  104  extend through the side wall of the distributor tube  102 . FIG. 11, which is a cross sectional view of the distributor tube  102  taken along line  11 — 11  of FIG. 10, illustrates a representative aperture  104 . Each aperture  104  at least partially defines the reactant air flow path through the metal-air battery  220 . 
     Referring to FIG. 9, the ventilation passageways  230  and  234  function to ensure that air flowing along the reactant air flow path is evenly distributed between metal air cells  60   a-f , as discussed above. Further, the ventilation passageways  230  and  234  also preferably function to allow a sufficient amount of air to flow through the reactant air flow path while the fan  70  (FIG. 5) is operating so that a large power output can be obtained from the metal-air cells  60   a-f . Further, the ventilation passageways  230  and  234  are preferably constructed so that the ventilation passageways provide a barrier function while the fan  70  is not operating. Regarding the barrier function in greater detail, the ventilation passageways  230  and  234  function so that air flow through the reactant air flow path is restricted while the fan  70  is not operating. As a result, a minimal amount of oxygen moves into the battery chamber  54  while the fan  70  is not operating. Further, the ventilation passageways  230  and  234  remain unsealed while the fan  70  is off or otherwise not supplying air to the metal-air battery  20 . That is, the reactant air flow path continues to define a passageway to the metal-air cells  60   a-f  while the fan  70  is off or otherwise not supplying air to the metal-air battery. For example, the reactant air flow path is not closed  25  by air doors or the like. The ventilation passageways  230  and  234  are operative, while the fan  70  is not supplying air to the metal-air battery  220 , for restricting air flow to the metal air cells  60   a-f  so that the metal-air battery  220  is capable of having a long shelf life without requiring a door or doors, or the like, to seal the ventilation passageways. 
     The barrier function of the ventilation passageways  230  and  234  is preferably the result of the sizing of the ventilation passageways. Each of the ventilation passageways  230  and  234  preferably has one or more sections that provide the barrier function, and those sections are referred to as barrier sections. For example, the inlet opening  32  (FIG. 1) may be a barrier section, the outlet opening  34  (FIG. 1) may be a barrier section, the portion of the inlet distributor tube  102   a  between the inlet opening  32  and the  35  aperture  104  most proximate to the inlet opening  32  may be a barrier section, the portion of the outlet distributor tube  102   b  between the outlet opening  34  and the aperture  104  most proximate to the outlet opening  34  may be a barrier section, or each of the apertures  104  may be a barrier section. Alternatively, it may be the case that each of the portions of the ventilation passageways  230  and  234  cooperate to provide the barrier function. 
     Each barrier section of the ventilation passageways  230  and  234  has a width that is generally perpendicular to the flow path therethrough, and a length that is generally parallel to the flow path therethrough. The length is greater than the width, and more preferably the length is greater than about twice the width. The use of larger ratios between length and width of the barrier sections of the ventilation passageways  230  and  234  is preferred, and depending upon the nature of the battery  220  the ratio can be more than 200 to 1. However, the preferred ratio of length to width of the barrier sections of the ventilation passageways  230  and  234  is about 10 to 1. 
     It is preferred for the apertures  104  to be barrier sections of the ventilation passageways  230  and  234 . That is, and referring also to FIG. 11, for each aperture  104  the length “L 2 ” is preferably greater than the width “W 2 ,” and more preferably the length is greater than about twice the width. More specifically, the use of larger ratios between length and width of the apertures  104  may be preferred, especially when the inside diameters of the inlet opening  32  (FIG.  1 ), the outlet opening  36  (FIG.  1 ), and the distributor tubes  102   a  and  102   b  are large such that solely the apertures  104  provide the barrier function that restricts air flow through the reactant air flow path while the fan  70  (FIG. 5) is not supplying air to the metal-air battery  220 . 
     Depending upon the nature of the battery  220 , the length to width ratio of the apertures  104  can be more than 10 to 1. However, the preferred ratio of length to width is about 2 to 1. The apertures  104  each may have a length of about 0.02 to 0.2 inches, with about 0.04 to 0.08 inches preferred, and a width of about 0.01 to 0.1 inches, with about 0.09 to 0.19 inches preferred. The total open area of each aperture  104 , measured perpendicular to the flow path therethrough, is therefore about 0.00008 to 0.008 square inches. 
     The preferred total open area of the apertures  104  depends upon the desired capacity of the battery. Any number of apertures  104  can be used such that aggregate open area of all of the apertures  104  equals this preferred total open area, with each such aperture preferably having the same or similar ratios of length to width to provide the desired flow distribution and/or barrier functions. Those skilled in the art will appreciate that the length of the apertures  104  may be increased, and/or the width decreased, if the differential pressure created by the fan  70  is increased. A balance between the differential pressure created by the fan  70  and the dimensions of the apertures  104  can be found at which the desired flow distribution and/or barrier functions are achieved. Whereas increasing the total open area of the apertures  104  will allow more air to flow through the metal-air battery  220  in response to operation of the fan  70 , it is preferred to maintain the number, size, and length-to-width rations of the apertures  104  (or other barrier section(s)) within a range that 19 provides the desired barrier function. Although the use of circular apertures  104  is disclosed, any conventional shape having the required ratios may be employed. Further, the apertures  104  may be straight or curved in length. 
     FIG. 12 is a diagrammatic view of a metal-air battery  320  exploded away from an electronic device  322  in accordance with a third exemplary embodiment of the present invention. The electronic device  322 . is identical to the electronic device  22  illustrated in FIG. 1, except for noted variations and variations that will be apparent from the following description. As illustrated in FIG. 12, one of the walls defining the docking cavity  342  of the docking station  340  defines an upstream opening  112  of an upstream ventilation passageway  110 . Similarly, another of the walls defining the docking cavity  342  defines a downstream opening  116  of a downstream ventilation passageway  114 . 
     The metal-air battery  320  can be identical to any of the previously discussed metal-air batteries, except for the noted variations and variations that will be apparent from the following description. For the metal-air battery  320  the inlet opening  332  of the inlet ventilation passageway  330  is defined through a side wall of the battery cover  328 . Similarly, the outlet opening  336  of the outlet ventilation passageway  334  is defined through an opposite side wall of the battery cover  328 . While the metal-air battery  320  is installed in the docking cavity  342 , the upstream opening  112  is contiguous and communicating with the inlet opening  332 , and the downstream opening  116  is contiguous and communicating with the outlet opening  336 . As a result, and as will be discussed in greater detail below, the upstream ventilation passageway  110  is an upstream extension of the reactant air flow path defined through the metal-air battery  320 , and the downstream ventilation passageway  114  is a downstream extension of the reactant air flow path defined through the metal-air . battery  320 . Gaskets or other conventional means can be used to minimize undesirable leakage at the interfaces between the respective openings  112 ,  332 ,  116  and  336 . Some sort of clamping device may be utilized to clamp the metal-air battery  320  to the docking station  340  in a manner that minimizes undesirable leakage at the interfaces between the respective openings  112 ,  332 ,  116  and  336 . 
     FIG. 13 is a diagrammatic cross-sectional view of the electronic device  322  taken along line  13 — 13  of FIG.  12 . The upstream ventilation passageway  110  includes an upstream tube  118  communicating with an intake cavity  120  that communicates with the environment exterior to the electronic device  322  through screening or an intake grating  122 . The downstream ventilation passageway  114  includes a downstream tube  124  communicating between the downstream opening  116  and a discharge cavity  126  that  35  communicates with the environment exterior to the electronic device  322  through a screening or a discharge grating  128 . An air moving device, such as a fan  129 , is within the intake cavity  120 . The fan  129  includes braces  130  that support a motor  132  that drives an impeller  134 . The tubes  118  and  124  may be shaped and sized in the same manner as the tubes  56  and  58  (FIG. 2) to provide a barrier function. 
     FIG. 14 is a diagrammatic side cross-sectional view of the metal-air battery  320  taken along line  14 — 14  of FIG.  12 . The metal-air battery  320  can be identical to any of the above discussed metal-air batteries except for the variations noted and variations that will be apparent from the following description. The metal-air battery  320  preferably does not include an air moving device. In embodiments where the ventilation passageways  330  and  334  of the metal-air battery  320  include tubes  136  and  138 , those tubes  136  and  138  can be identical to the tubes  56  and  58  (FIG. 2) or the tubes  102   a  and  102   b  (FIGS.  9 - 11 ),  10  except that the upper portions of the tubes  136  and  138  are bent and mounted to a respective side wall of the battery cover  328  so that they are in communication with and contiguous with their respective opening  332  or  336  (FIG.  12 ). As illustrated in FIG. 14, the metal-air battery  320  includes the distributor plate  66 , such that the tubes  136  and  138  preferably resemble the tubes  56  and  58  (FIG.  2 ). Alternatively, the metal-air battery  320  does not include the distributor plate  66 , in which case the tubes  136  and  138  preferably resemble the tubes  102   a  and  102   b  (FIG.  9 ). Alternatively, the distributor plate  66 , and not the tubes  136  and  138 , may be included in the metal-air battery  320  when the tubes  118  and  124  of the electronic device  322  are shaped and sized in the same manner as the tubes  56  and  58  (FIG. 2) to provide the barrier function. 
     While the metal-air battery  320  is installed within the docking cavity  342 , the reactant air flow path of the metal-air battery  320  originates from the ambient environment external to the electronic device  22 . The reactant air flow path then extends through the intake cavity  120  and the upstream ventilation passageway  110  of the electronic device  322 . The reactant air flow path then extends through the inlet ventilation  25  passageway  330 , through the battery chamber  54 , and then through the outlet ventilation passageway  334  of the metal-air battery  320 . Then the reactant air flow path extends through the downstream ventilation passageway  114  and the discharge cavity  126  of the electronic device  322 . 
     Operation of the fan  129  may be controlled as described above with respect to the fan  70  (FIG.  5 ). Operation of the fan causes air to flow along the reactant air flow path so that air is supplied to the metal-air cells  60   a-f . The fan  129  may further supply air through other passageways to provide cooling air flow, or other air flow, to components of the electronic device  322 . In summary, there are numerous configurations in which the barrier function is provided for the metal-air battery  320  while the fan  129  is not supplying air to the battery. The fan may not be supplying air to the battery by virtue of the fan being off, the fan not being associated with the battery (for example see FIG.  12 ), or the air flow being created by the fan may not be routed to the battery. 
     In accordance with an alternative embodiment, the battery housing  324 , or the like, remains attached to the docking station  340 . A door, or the like, is provided in the battery housing so that solely the stack of metal-air cells  60   a-f  can be removed from and reinstalled in the battery housing. 
     FIG. 15 is a diagrammatic side cross-sectional view of a metal-air battery  420  and FIG. 16 is a diagrammatic cross-sectional view of the metal-air battery  420  taken long line  16 — 16  of FIG. 15, in accordance with a fourth exemplary embodiment of the present invention. The metal-air battery  420  is identical to the metal-air battery  20  (FIGS. 1-3 and  5 ), except for noted variations and variations that will be apparent from the following description. 
     The metal-air battery  420  defines a recirculating reactant air flow path which is illustrated by broken-line arrows in FIG.  15 . Air flows along the recirculating reactant air flow path in response to operation of an air moving device, such as the fan  470 . The fan  470  includes a motor and impeller that are within a rectangular housing. The distributor plate  66  functions to distribute air flowing along the recirculating reactant air flow path so that air flow, and therefore oxygen, is evenly distributed between metal-air cells  60   a-f  contained within the battery chamber  454 . 
     The battery chamber  454  is separated into what can be characterized as an upstream chamber  140 , which is primarily proximate to the upstream ends of the metal-air  20  cells  60   a-f , and a downstream chamber  142 , which is primarily proximate to the downstream ends of the metal-air cells. The upstream chamber  140  and the downstream chamber  142  are separated by the metal-air cells  60   a-f , the plenums  64   a-c , the fan  470 , and a barrier plate  66 . As illustrated in FIGS.  15 — 16 , portions of the upstream chamber  140  and downstream chamber  142  are above and partially bounded by the closed wall  59  (FIG. 7) of the metal-air cell  60 a, and those chamber portions are separated by the fan  470  and the distributor plate  66 . The fan  470  includes an inlet  146 , and a portion of the inlet  146  is covered by the closed wall  59  of the metal-air cell  60   a  whereas the uncovered portion of the inlet  146  communicates with the downstream chamber  142 . The fan  470  further includes an outlet  148  that communicates with the upstream chamber  140 . The inlet tube  456  is hidden from view behind the outlet tube  458  and a portion of the fan  470  in FIG.  15 . 
     The upstream end of the inlet tube  456  of the inlet ventilation passageway  430  communicates with and is contiguous with the inlet opening of the inlet ventilation passageway  430 . The inlet opening of the inlet ventilation passageway  430  is not shown (but, for example, see the inlet opening  32  of FIG. 1) but is positioned to directly communicate with the ambient environment while the metal-air battery  420  is installed to the docking station  40  (FIG.  1 ). The downstream end of the inlet tube  458  communicates with the downstream chamber  142 . 
     The downstream end of the outlet tube  458  of the outlet ventilation passageway  434  communicates with and is contiguous with the outlet opening of the outlet ventilation passageway  434 . The outlet opening of the outlet ventilation passageway  434  is not shown (but for example see the outlet opening  36  of FIG. 1) but is positioned to directly communicate with the ambient environment while the metal-air battery  420  is installed to the docking station  40  (FIG.  1 ). The upstream end of the outlet tube  456  communicates with the outlet  148  of the fan  470 . 
     The inlet tube  456  and outlet tube  458  may be sized and function in the same manner as the inlet and outlet tubes  56  and  58  (FIG. 2) of the first exemplary embodiment, except more preferably the inlet tube  456  has a length of about 1.5 to 3.5 inches, with about 3.0 inches preferred, and the outlet tube  458  has a length of about 1.0 to 2.5 inches, with about 2.0 inches preferred. 
     The fan  470  preferably operates in response to the voltage of the metal-air cells  60   a - 60   f  of the metal-air battery  420  in the same manner as described above with respect to the first exemplary embodiment. While the fan  470  is operating, a portion of the air being moved by the fan includes air that is drawn into the downstream chamber  142  through the inlet ventilation passageway  430 , and another portion of the air being moved by the fan includes air that is forced out of the battery chamber  454  by way of the outlet ventilation passageway  434 . The operating fan  470  further causes air to recirculate from the downstream chamber  142  to the upstream chamber  140 , and the distributor plate  66  is in the path of that recirculating air and functions to distribute the recirculating flow of air so that air flow, and therefore oxygen, is evenly distributed between metal-air cells  60   a-f  contained within the battery chamber  454 . The air that enters the battery chamber  54  through the inlet tube  56  refreshes the recirculating air. 
     The ventilation passageways  430  and  434  may be arranged to communicate with the ambient environment by way of ventilation passageways resembling the ventilation passageways  110  and  114  (FIG. 13) and defined by an electronic device capable of receiving and being powered by the metal-air battery  420 , as should be understood by those skilled in the art upon understanding this disclosure. 
     A further embodiment of the present invention is shown in FIG.  17 . This embodiment shows an electronic device  750  powered by a metal-air battery  760 . The electronic device  750  includes an intake diffusion tube  770  with an internal fan  780 . The intake diffusion tube  770  is in communication with the atmosphere and the metal-air battery  760 . The electronic device  750  also includes a positive and a negative battery terminal  790 . Similarly, the metal-air battery  760  includes an intake diffusion tube  800  that is sized to mate with the intake diffusion tube  770  of the electronic device  750 . The metal-air battery  760  also includes an exhaust diffusion tube  810  vented to the atmosphere or, alternatively, back through the electronic device  750 . The metal-air battery also has a positive and a negative battery terminal  820 . The metal-air battery  760  is sized to fit within or adjacent to the electronic device  750  such that the respective diffusion tubes  770 ,  800  and the respective battery terminals  790 ,  820  are in contact and communication. 
     The battery  760  and the electronic device  750  may be coupled in the manner described in connection with the embodiment of FIG.  12 . Another method of coupling the battery  760  and the electronic device  750  is shown in co-pending commonly-owned application entitled “Air-Managing System For Metal-Air Battery Using Resealable Septum” (Ser. No. 09/321,352), entitled “Replaceable Metal-Air Cell Pack With Self-Sealing Adaptor”. 
     In use, air is drawn into the intake diffusion tube  770  of electronic device  750  by the fan  780 . The air then passes into the metal-air battery  760  via the intake diffusion tube  800  and circulates through the metal-air battery  760 . The air then passes out of the exhaust diffusion tube  810  back to the atmosphere. Electric power is provided to the electronic device  750  from the metal-air battery  760  via the respective battery terminals  820 ,  790 . By placing the fan  780  within the electronic device  750 , as opposed to within the metal-air battery  760  itself, a relatively small metal-air battery  760  is possible. The battery  760  is both small and relatively inexpensive to replace because the fan  780  is stationary within the electronic device  750  and need not be replaced each time the battery  760  is exhausted. Further, because the metal-air battery  760  has an intake diffusion tube  800  and an exhaust diffusion tube  810 , the battery  760  is properly isolated from the environment during periods of non-use. 
     FIGS. 19 and 20 show an isolating or a diffusion pathway in the shape of a diffusion tube  500  for use with the embodiment of FIG. 17, or with other embodiments of the present invention. The diffusion tube  500  may be used with the plurality of cells enclosed within the housing of the metal-air battery  760  or any conventional type of metal-air cell or battery. The diffusion tube  500  is preferably, but not necessarily, cylindrical. Any cross-sectional shape that provides the desired isolation is suitable. As with the diffusion tubes described in U.S. Pat. No. 5,691,074, the diffusion tube  500  is sized to eliminate substantially air flow therethrough when a fan  510  or an air mover is turned off while permitting adequate air flow therethrough when the fan  510  is on. Specifically, the diffusion tube  500  has a length of greater dimension than its width, and more preferably, the length is greater than about twice the width. The use of larger ratios between length and width are preferred. Depending upon the nature of the metal-air cells, the ratio can be more than 200 to 1. However, the preferred ratio of length to width is about 10 to 1. 
     Positioned within the diffusion tube  500  is the fan  510 . The fan  510  is a conventional air moving device. For example, although the term “fan”  510  is used herein, the air movement device may include other conventional devices such as a pump, bellows, and the like known to those skilled in the art. The fan  510  includes a plurality of fan blades  520  driven by a conventional electric motor  530  or similar device. The electric motor  530  draws power from the cell or the battery itself. The fan  510  is positioned within the diffusion tube  500  by one or more support struts  540  or similar types of anchoring devices. The support struts  540  anchor the fan  510  within the middle of the diffusion tube  500 . By placing the fan  510  within the diffusion tube  500 , the fan  510  moves air through the diffusion tube  500  much in the same manner as a blade moves air within a turbine. 
     In accordance with a first exemplary embodiment of the present invention, the diffusion tube  510  functions as both an inlet and an outlet because fan  510  causes reciprocating airflow through the diffusion tube  500 . In an alternating fashion, ambient air flows through the diffusion tube  500  toward the cells or the oxygen electrodes while air that is at least partially depleted of oxygen flows through the diffusion tube  500  away from the cells  15  or the oxygen electrodes. Further, multiple diffusion tubes  510  can be utilized in the aggregate such that the diffusion tubes  500  function in unison as inlets, and thereafter function in unison as outlets, in an alternating fashion. When air is provided to the cells  15  or the oxygen electrodes by a reciprocating airflow through one or more diffusion tubes  500 , it is preferable for the fan  510  to cause at least some mixing of air proximate to the cells or the oxygen electrodes. This mixing ensures that the cells or the electrodes are exposed to a relatively uniform distribution of oxygen. Of course, to cause such mixing, the volume of the incoming air flow must be greater than the volume of the diffusion tube itself. 
     In accordance with a second exemplary embodiment of the present invention, at least two diffusion tubes  500  are utilized to provide airflow to the cells in response to operation of fan  510 . The diffusion tubes  500  and the fan  510  are arranged so that one of the diffusion tubes  500  functions as an inlet through which ambient air flows toward the cells or the oxygen electrodes and another of the diffusion tubes  500  functions as an outlet through which oxygen depleted air flows away from the cells or the oxygen electrodes. Further, a first group of diffusion tubes  500  may function together as inlets and a second group of diffusion tubes  500  may function together as outlets. 
     FIG. 18 shows an AA size cell  900 . The cell  900  has an air manager cap  910  with a cap diffusion tube  920  extending from an air inlet  930  communicating with the atmosphere to a cap mating connector  940 . Positioned within the cap diffusion tube  920  is a fan  950  or other types of air movement devices similar to that described above. The fan  950  may be capable of producing a reciprocating airflow. The air manager cap  910  also includes a positive cell terminal  960  and a cap battery connector  970 . The cell  900  further includes a replaceable chemistry body  980  for mating with the air manager cap  910 . Positioned within the chemistry body  980  may be a zinc paste anode material  990 , a separator layer  1000 , and a cathode layer  1010 . The zinc paste anode material  990 , the separator layer  1000 , and the cathode layer  1010  are of conventional design. The zinc paste anode material  990  is kept in contact with the separator layer  1000  via a spring-loaded gantry  1020  or other types of conventional compressible elements to maintain a mechanical interface with the zinc paste. The chemistry body  980  also includes a body diffusion tube  1030 . The body diffusion tube  1030  extends from a body mating connector  1040  designed to mate with the cap mating connector  940  to an air outlet  1050  positioned adjacent to the cathode layer. The chemistry body  980  also includes a negative cell terminal  1060  and a body battery connector  1070 . 
     In use, air is drawn into the cell  900  through the cap diffusion tube  920  in the air manager cap  910  via the air inlet  930 . The air is drawn into the cap diffusion tube  920  via the fan  950  positioned therein. The air passes through the cap diffusion tube  920  and into the chemistry body  980  and the body diffusion tube  1030  via the respective mating connectors  940 ,  1040 . The air then exits the air outlet  1050  adjacent to the cathode layer  1010 . After a sufficient amount of intake air has been forced into the chemistry body  980 , the fan  950  may reverse direction. Exhaust air is then forced into the air outlet  1050 , through the respective diffusion tubes  920 ,  1030  and out of the air inlet  930 . After the zinc paste anode material  990  is exhausted, the chemistry body  980  may be removed from the air manager cap  910 . The air manager cap  910  may then be attached to a fresh chemistry body  980 . Current flows through the cell  900  via the respective battery connectors  970 ,  1070 . The cell  900  may provide electrical power to a circuit via the respective cell terminals  960 ,  1060 . 
     Either both of the respective diffusion tubes  920 ,  1030  or only the body diffusion tube  1030  may serve as the isolating pathway for the cell  900  as a whole. Because the body diffusion tube  1030  acts as an isolating pathway, the chemistry body  980  may have a long shelf life without being sealed or connected to the air manager cap  910 . Alternatively, the cap diffusion tube  920  may act as the isolating pathway if the body diffusion tube  1030  is sealed when not connected to the air manager cap  910 . Numerous variations on this embodiment may be used. For example, the chemistry body  980  may use both an intake and an exhaust diffusion tube as opposed to a reciprocating fan. 
     The preferred capacity of the diffusion tubes described herein for passing airflow in response to operation of fan in the various embodiments depends upon the desired capacity of the metal-air cells. Any number diffusion tubes can be used such that the aggregate airflow capacity of multiple diffusion tubes equals a preferred total airflow capacity. Those skilled in the art will appreciate that the length of the diffusion tubes may be increased, and/or the diameter decreased, if the differential pressure created by the air-moving device is increased. A balance between the differential pressure created by the air moving device and the dimensions of diffusion tubes can be found at which airflow and diffusion through diffusion tubes will be sufficiently reduced when the air moving device is not forcing air through the diffusion tube. 
     Whether utilized for one-way flow or reciprocating flow, the diffusion tubes as described herein may be isolating passageways as described above and in commonly owned U.S. Pat. No. 5,691,074. The terms “diffusion tubes” and “isolating passageway” are used synonymously herein. The isolating passageways are sized to (i) pass sufficient airflow therethrough in response to operation of the fan or the air moving device so that the metal-air cells provide an output current for powering a load, but (ii) restrict airflow and diffusion while the diffusion tubes are unsealed and the fan is not forcing airflow therethrough, so that the cells or the oxygen electrodes are at least partially isolated from the ambient air. The diffusion tubes maintain a constant humidity level such that the internal water vapor protects the oxygen electrodes of the cell. These diffusion tubes preserve the efficiency, power and lifetime of the metal-air cells. Each diffusion tube provides an isolation function while at least partially defining an open communication path between the ambient air and the cells or the oxygen electrodes. The diffusion tubes therefore provide an isolation function without requiring a traditional air door or doors, or the like, to seal the diffusion tubes. 
     Although the diffusion tubes restrict airflow and diffusion while the fan is not forcing airflow therethrough, it is desirable in some systems to permit a limited amount of diffusion through the diffusion tubes while the fan is not on. For example, for secondary or rechargeable metal-air cells it is preferred for the diffusion tubes to allow for diffusion of oxygen away from the cells or the oxygen electrodes to the ambient environment. As another example, in some circumstances it is desirable for at least a limited amount of oxygen to diffuse from the ambient air through the diffusion tubes to the oxygen electrodes. This diffusion maintains a consistent “open cell voltage” and minimizes any delay that may occur when the metal-air cells transition from a low or no current demand state to a maximum output current. 
     The diffusion tubes are preferably constructed and arranged to allow a sufficient amount of airflow therethrough while the fan is operating so that a sufficient output current, typically at least 50 ma, and preferably at least 130 ma, can be obtained from the metal-air cells. In addition, the diffusion tubes are preferably constructed to limit the airflow and diffusion therethrough such that the leakage or drain current that the metal-air cells are capable of providing while the fan is off is smaller than the output current by a factor of about 50 or greater, as described above. In addition, diffusion tubes are preferably constructed to provide an “isolation ratio” of more than 50 to 1, as described above. Such isolation ratios provide a relatively high powered metal-air battery with a longer shelf life. Further, the volumetric energy density of the battery as a whole may be increased because the volume of space allocated to the air plenum and the fan may be reduced. 
     It should be understood that the foregoing relates only to exemplary embodiments of the present invention, and that numerous changes may be made therein without departing from the scope of the invention as defined by the following claims.