Patent Publication Number: US-2010108291-A1

Title: Method and apparatus for embedded battery cells and thermal management

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/191,846, filed on Sep. 12, 2008, and U.S. Provisional Application No. 61/194,382, filed on Sep. 26, 2008 for Embedded Battery Cells and Thermal Management of Personal Computers by Per Onnerud, Phillip E. Partin, Scott Milne, Yanning Song, Richard V. Chamberlain, II, and Nick Cataldo, the teachings of both of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Portable computers (or notebooks) typically include a single main battery that is charged and stores energy from an external alternating current to a direct current (AC/DC) adapter. Currently the main battery is a lithium ion battery and adds approximately one pound to the overall weight of the portable computer. The main battery degrades and may need to be replaced in one to five years. Degradation of the main battery may be due to use or due to failures in the cooling systems of the portable computer. Failures in the cooling system (e.g., a fan or heatsink) may be caused by collection of dust and debris, which will cause the entire portable computer to get hotter and hotter to the touch and for the cooling system to become louder over time. 
     SUMMARY OF THE INVENTION  
     The summary that follows describes some of the example embodiments included in this disclosure. The information is proffered to provide a fundamental level of comprehension of aspects of this disclosure. 
     An example embodiment of the present invention includes a portable computer and corresponding method. The portable computer may include at least one heat generating component and a battery cell thermally coupled to the at least one heat generating component. The heat generating component may be a processor, e.g., a central processing unit (CPU) chip or a graphics processing unit (GPU) chip, which may be thermally bonded to the battery cell. The battery cell may be a prismatic aluminum cell or a positive electrode. The battery cell may be oriented under the palm rest of the portable computer. The battery cell may have a heat capacity that is greater (e.g., at least an order of magnitude greater) than the heat capacity of the heat generating component. A thermal attachment block or heat pipe may be thermally coupled between the at least one heat generating component and the battery cell. 
     Another example embodiment of the present invention includes at least one radiating wall of the battery cell having an enhanced surface area with extruded heat sink/features (e.g., fins, pins, or the like). Additionally, the battery cell may be coupled to a cooling assembly, which may include a fan to direct airflow across the radiating wall of the battery cell. The battery cell may also be enclosed in a shield to protect the battery cell from direct heat radiation. 
     An example embodiment of the present invention may also include a motherboard of the portable computer and the battery cell may be coupled to the motherboard, for example, using a clip to allow for detachment. 
     A battery cell may be embedded within the motherboard of the computer in another example embodiment of the present invention. The battery cell may also be located on top of, within, or spanning the motherboard of the portable computer. 
     Another example embodiment of the present invention may include a plurality of cells within a battery cell pack housing and coupled to the at least one heat generating component. The cell pack housing may be located under the palm rest of the portable computer. 
     An example embodiment of the present invention may include charge management control that preferentially charges the battery cell during times when cooling is required. 
     Another example embodiment of the present invention may include additional portable computer components (e.g., hard disk, optical drive, etc.) that are enclosed in a shield and the shield is configured to protect the hard disk from direct heat radiation. 
     An example embodiment of the present invention may also include a plurality of cells distributed within a portable computer housing and each of the plurality of cells are individually, thermally coupled to the at least one heat generating component. The plurality of cells may be individually enclosed in a shield to protect from direct heat radiation. The plurality may also be coupled to a motherboard of the portable computer, for example using at least one clip to allow for detachment. The plurality may be comprised of prismatic aluminum cells and located under the palm rest of the portable computer. 
     Current notebook personal computers (or notebook PC) typically include an external battery that is enclosed in a plastic case and designs attempt to minimize heat transfer from the notebook to the battery pack because heat is known to degrade battery cells in their present form. Embodiments of the present invention may allow for battery cells to be embedded into the notebook PC design and for the embedded battery cells to act as a heat sinks if a means exists for transporting the heat out of the notebook PC. The battery cells may be adjacent to surfaces made out of material having high thermal conductivity, e.g., metal, engineered thermal materials, or the like. Using the embedded battery cells may minimize the amount and size of dedicated heat sinks, heat pipes, fans and other means of thermal management inside the notebook PC. The reduction of the need for both passive and active thermal management inside the notebook PC saves cost, space, and allows the manufacturer of the notebook PC to have more freedom in the overall designing process. 
    
    
     
       BRIEF DESCRIPTION  
         FIGS. 1A-1C  illustrate several configurations for thermal management using a notebook heat transfer and dissipation device of a portable computer that may be employed in accordance with an embodiment of the present invention; 
         FIGS. 2A-2F  illustrate several configurations of a circuit board mounted notebook battery that may be employed in accordance with an embodiment of the present invention; 
         FIGS. 3A-3C  illustrate several configurations of a distributing battery cells within a portable computer in accordance with an example embodiment of the present invention; 
         FIGS. 4A and 4B  illustrate a comparison of contact surface area of an oblong cell battery and two 18650 cells; 
         FIGS. 5A-5C  illustrate battery cell can designs that may be modified for improved heat transfer in accordance with an example embodiment of the present invention; 
         FIG. 6  depicts an algorithm that may be employed for cooling a central processing unit within the personal computer in accordance with an example embodiment of the present invention; and 
         FIGS. 7-9  illustrate exploded views of battery packs that may be employed in accordance with an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
     The present application is directed to a device comprising: at least one heat generating component and a battery cell thermally coupled to the at least one heat generating component. The device may be portable. The battery cell may be rechargeable, which includes lithium in a cathode of the battery. 
     Several configurations of the present invention for thermal management of a device using a battery are illustrated in  FIGS. 1A-1C . Each configuration involves using a battery as a thermal heat transfer channel (e.g., heat transfer  108  of  FIG. 1A ) from CPU/GPU chip to extruded features (e.g., radiating fins or extruded heat sink  109  of  FIG. 1A ). 
       FIG. 1A  illustrates battery  107  attached to a CPU/GPU chip  105 , which is the heat generating component, via a thermal attachment block  103 . At another location, battery  107  is attached to the radiating fins or extruded heat sink  109 . Heat is transferred  108  from CPU/GPU chip  105 , through battery  107  to radiating fins  109 . Fan  111  may be additionally be employed to increase air flow  112  across the radiating fins  109 . A benefit of using a battery  107  for thermal transfer is reduction or elimination of need for other heat transfer channels (such as a heat pipe  148  of  FIG. 1C  or other thermally conducting structures) in the portable computer. As a result, the cost of materials and manufacturing complexity can be significantly reduced. The overall size of the thermal management solution is reduced, so the size of the notebook may be reduced. 
     Another configuration shown in  FIG. 1B  includes the addition of radiating fins or extruded features  129  at the surface of a battery  127 , which may increase the surface area of the battery  127  and provide increased dissipative heat transfer from the battery  127  into the surrounding air. Here, the battery  127  is serving a thermal dissipative function. Air fan  131  may be configured to blow air  132  across the battery  127  in a way to increase the heat dissipation effect. A thermal attachment block  123  may be used to attach battery  127  to CPU/CPU chip  125 . In  FIG. 1B , for example, battery  127  is in close proximity to the CPU/GPU chip  125 , which improves compactness of the overall portable computer design. 
       FIG. 1C  shows the addition of heat pipe  148  to allow placement of a battery  147  in a variety of locations in the device&#39;s enclosure which may include, for example, extending the battery  147  to the edge of the portable device&#39;s enclosure where the battery  147  will dissipate excess heat to the atmosphere. Battery  147  may be employed in a heat-dissipative configuration because the battery  147  has radiating fins or extruded features  149  on a surface of the battery  147 . The battery  147  may have additional heat-dissipative features because it has a significantly greater volumetric heat capacity as compared to the heat of the CPU/GPU chip  145 , and because CPU/GPU chip  145  operates at a lower temperature than battery  147 . Further, battery  147  can dissipate heat more rapidly than CPU/GPU chip  145  by virtue of the materials of construction of battery  147 , such as the container component of battery, within which the electrodes and electrolyte of battery  147  reside. 
     The present application is also directed to a portable computer comprising at least one heat generating component and a battery cell thermally coupled to the at least one heat generating component. The heat generating component may be a processor (e.g., central processing unit chip or graphics processing unit chip), which may be thermally bonded to the battery cell. As used herein, “thermally bonded” means a pathway for thermal conduction, such as between a heat source and a battery that is better than what would occur in the absence of the pathway, while continuing to maintain electrical insulation between these same components. Examples include the use of thermally conductive epoxy, adhesive or electrical insulator film materials. Common terms for some such materials include “gap filler” and “gap pads” that describe the role of such materials to allow for efficient heat conduction between two components, such as a heat source and battery, without creating an electrically conducting path. This would allow taking advantage of the heat sink properties of the battery as described in this invention. Some examples of acceptable materials for thermal bonding include, but is not limited to, multiple Bergquist products, for example, Sil-Pad, Gad Pad, and Gap Filler brand name products, as well as multiple Emerson &amp; Cuming products, such as, Stycast brand name epoxy. The battery cell may be a prismatic aluminum cell. The heat capacity of the battery cell is greater than the heat capacity of the heat generating component, such that the heat capacity of the battery cell is at least an order of magnitude greater than the heat capacity of the heat generating component. The portable computer may also include charge management control that preferentially charges the battery cell during times when cooling of the at least one heat generating component is required. 
     The battery cell may have at least one radiating wall, which includes an enhanced surface area. The radiating wall may include fins, pins, extruded features or the like. The battery cell may be coupled to a cooling assembly, which includes a fan to direct airflow across the radiating wall of the battery cell. 
       FIGS. 2A through 2F  illustrate example configurations of a portable computer comprising at least one heat generating component and a battery cell thermally coupled to the at least one heat generating component in accordance with an embodiment of the present invention. 
     As shown in  FIG. 2A , battery  205  can be embedded in a portable computer by mounting on or within the printed circuit board (or circuit board)  201 . Battery  205  may be electrically connected to conductive layers in the printed circuit board  205  to provide access to its stored electrical energy. Battery  205  is thermally connected to CPU/GPU  203  on the printed circuit board  201  to enable dissipation of excess heat using conductive layers in the printed circuit board  201 . 
     Alternatively,  FIG. 2B  illustrates heat piping techniques commonly employed in the industry to allow remote placement of a battery  215  with respect to CPU/GPU  213 , for example, to transfer heat from inside the portable computer to an edge where battery  215  is positioned to radiate heat to the atmosphere. An embedded lithium ion battery may be used for thermal management in a portable computer. In addition to its electrical energy storage function, the embedded battery may transfer and dissipate excess heat generated by chip devices on the portable computer&#39;s circuit board, such as the CPU and GPU. The use of portable computer batteries to provide thermal management in the portable computer offers many benefits to the manufacturer and end user. For example, thermal management component count is reduced or eliminated, which results in material and manufacturing cost savings. Fewer components in the notebook reduce its physical size and weight. Design flexibility is increased as batteries may be placed in closer proximity to heat generating components. 
     A portable computer may also include the motherboard of the portable computer and the battery cell may be coupled (e.g., using at least one clip) to the motherboard of the portable computer.  FIG. 2C  illustrates that a battery  225  can be incorporated as a component of printed circuit board  221 . Removing the need for traditional battery pack packaging will reduce materials cost, space and weight requirements for the portable. The elimination of traditional thermal management components further reduces cost, size and complexity of the portable computer. A soldering connection technique between battery  205  and the circuit board  221  is designed to provide two paths, one path  222   a  to transfer stored electrical energy from the battery  225  to the circuit board  221  and a second path  222   b  to transfer thermal energy from thermal conduction layers in circuit board  221  to battery  225 . In the case of a permanently mounted battery, shown in  FIG. 2C , thermal connection  224  is formed to a large pad on the surface of circuit board  221  which is in turn connected to thermal conduction layers in the board. The thermal connection  224  material thermally bonds the battery  225  to circuit board  221  may include one of the following: electrical solder, thermally conductive paste, or a thermally conductive engineered material. 
     The ability of designers to place batteries on the printed circuit board provides additional design flexibility. For example, the battery cell may be detached from the motherboard; the battery cell may be embedded within or located on top of or spanning the motherboard of the portable computer; or the battery cell may be oriented under the palm rest of the portable computer. Employment of configurations, or features, that permit removal of battery  235  from printed circuit board  231 , such as a compression clip  236 , as shown in  FIG. 2D , for example, enables service replacement of battery  105  during the lifetime of the notebook. The orientation of battery  235  with respect to circuit board  231  can be in a surface mounted orientation where battery  235  or battery mounting clips  246  are directly soldered to the surface of circuit board  231 . This orientation, shown in  FIG. 2D  (using compression clips  236 ) and  FIG. 2E  (using mounting clips  246 ) will be well-suited for surface mount circuit board manufacturing techniques, such as automated component placement and solder reflow used currently in the industry. Battery  245  or battery mounting clips  246  may, alternatively, be mounted in a region where circuit board  241  material has been removed, such that circuit board  241  surrounds some or all of the mounted battery  245 , such as is shown in  FIG. 2E . This orientation enables a more compact fitting of the battery with the circuit board by reducing the height of the battery to either side of the board by approximately half of the surface mounted orientation. 
     In another approach, the battery may be thermally coupled  254  directly to the surface of a printed circuit board  251 , as shown in  FIG. 2F . Thermal coupling as illustrated in  FIGS. 2C and 2F  may be done by welding a thermally conductive pad to couple a battery cell(s) to the PCB  221  (of  FIG. 2C ) or the CPU/GPU  253  (of  FIG. 2F ), which provides an additional benefit of allowing for mechanical vibration damping to suppress vibration of components within the housing of a personal computer. One or more lithium ion battery cells may be distributed in a desirable configuration within a portable computer so as to provide thermal management of excess heat generated by heat generating components, such as a CPU or GPU, in accordance with an example embodiment of the present invention. A benefit of distributing batteries throughout the portable computer in thermally advantageous locations may be to increase the portable computer design flexibility. Designers may have new options to place heat sensitive components that may also allow for added cost, size and weight saving. 
     Distributed notebook battery cells may be mounted to the circuit board using techniques described in the descriptions of  FIGS. 2A-2F . Using these mounting configurations, series and parallel electrical connections between the distributed cells may be established using conducting layers in the circuit board. Alternatively, cells may be mounted as part of the portable computer enclosure and connected in series or in parallel using discrete electrical bus wires or bars. 
     The portable computer may also include plurality of cells distributed within the housing of the portable computer. The plurality of cells may be individually, thermally coupled to the at least one heat generating component. The plurality of cells may also be individually enclosed in a shield, which protects the plurality of cells from direct heat radiation. In addition, the plurality of cells may be coupled (e.g., using at least one clip) to a motherboard of the portable computer. The plurality of cells may also be detached from the motherboard. The plurality of cells may be comprised of prismatic aluminum cells. The plurality of cells may also be located under the palm rest of the portable computer. The portable computer may also include a thermal attachment block that is thermally coupled between the at least one heat generating component and the battery cell. The portable computer may also include a heat pipe thermally coupled between the at least one heat generating component and the battery cell. 
       FIGS. 3A-3C  illustrate several configurations of a distributing battery cells within a portable computer in accordance with an example embodiment of the present invention. 
       FIG. 3A  illustrates the placement of battery cells  309   a - c  in selected locations to provide several thermal management roles, including dissipation of excess heat from inner locations to the edge of the notebook enclosure (or portable computer housing)  303 . In this placement, heat pipes  308   a - c  may be used to move heat to the remotely located radiating batteries  309   a - c,  respectively. Finned batteries, such as are shown in  FIGS. 1A-1C , in combination with fans, provide increased air flow. A heat attachment block  305  at the CPU  306  or GPU  307  may be employed to thermally interface the CPU  306 /GPU  307  with the heat pipe. For example, depending on the amount of heat emitted from a heat generating component, additional heat pipes can be connected to assist with heat dissipation, such as CPU chip  306  connected to heat pipes  308   a,    308   b.  Another placement, shown in  FIG. 3B , provides diffusion of heat from a localized component, such as CPU chip  326  or GPU chip  327 , to a larger surface area  323 , such as the top surface or bottom surface of the portable computer enclosure where it may be radiated outward. Battery cells  329   a - c  may act as thermal transfer paths to direct heat from CPU chip  306  and GPU chip  307 , by way of an attachment block  325 , to a larger surface area  323 . The attachment block  325  may enclose the CPU chip  326  and the GPU chip  327  to protect the chips from direct heat radiation. In addition, the larger surface area  323  can be, for example, a large stamped aluminum plate located underneath the keyboard, or at the bottom surface of the portable computer. Heat is then radiated from the larger surface area  323 . As such, the portable computer may also include a hard disk, which is enclosed in a shield and the shield protects the hard disk from direct heat radiation. The portable computer may also include an optical drive, which is enclosed in a shield and the shield is configured to protect the hard disk from direct heat radiation. 
     Another placement, shown in  FIG. 3C , provides thermal shielding between CPU  336  and GPU  337 , and heat sensitive devices (or components) inside the portable computer, such as a hard disk drive, optical drive, solid state memory, keyboard or other user-input devices and user-contact areas. The shielding provides protection to the component, for example, to prevent data loss in a hard drive or solid state memory due to excess heat exposure. CPU  336  may have several connections to battery cell  339   a,  and GPU chip  337  may have several connections to another battery cell  339   b  (connections represented as arrows). Thermal shielding occurs because battery cells  339   a,    339   b  are used to shield the temperature sensitive component  341  from the CPU chip  336  and the GPU chip  337 . 
       FIGS. 4A and 4B  illustrate a comparison of contact surface area of an oblong cell battery  400  and a battery  420  comprised of two cells. Typically, the container (or can) is of any suitable metal for fabricating a battery cell, such as stainless steel, aluminum, and nickel. Preferably, the material of the can is aluminum, which has relatively high thermal conductivity. Moreover, aluminum is relatively easy to configure into shapes that have high surface area, such as fins or corrugated surfaces. 
     As illustrated by  FIG. 4A , a battery  400  may be employed that has a relatively large surface area per unit of volume. The battery  400  is comprised of a can  405  that encapsulates the battery cell  410 . The top cap  415  provides a location upon which a positive tab may be connection (e.g., by welding) and a negative tab may be connected (e.g., by welding) onto a connection within the can  405  of the battery  400 .  FIG. 4   b  (prior art) illustrates a battery  420  that includes two 18650 battery cells  425 . The use of the oblong cell battery  400  allows for the development of additional useable space (when compared to the 18650 battery cells  425 ). In addition, the oblong battery cell  400  allows for the use of the space contained within a battery pack (e.g., see battery pack  710  of  FIG. 7 ) which allows for additional design capabilities. 
     As such, examples of suitable batteries for the present invention includes batteries having a high ratio of surface area to volume include batteries that have at least one relatively planar surface, such as prismatic battery cells, as illustrated by  FIG. 4A . Particularly suitable batteries are those that are less susceptible to rapid temperature increase when overcharged, and which typically will operate at relatively low temperature. A specific example of a suitable battery cell is a lithium-ion type battery cell, such as an aluminum case, prismatic-shaped cell with approximate dimensions of 18×37×65 mm, a nominal operating voltage of 3.7 V and an internal AC impedance of approximately 25 mΩ, capable of delivery a capacity of 4400 mAh at current rates up to 8.8 A, while operating at temperatures ranging from −20 to 60 C, available from Boston-Power, of Westborough, Mass. 
     In the embedded design, the can of the battery cell employed can be specially designed to have a larger, or enhanced, surface area for heat transfer. Two examples are shown, in  FIGS. 5A and 5B , of radiating pins extruding from at least one surface of the battery cell. Another embodiment is shown in  FIG. 5C . In these designs, the surface of the can is not smooth but with many small cooling fins or corrugated surface. These fins or corrugations help to dissipate the heat. 
     The present application is also directed to a method for using a battery cell to assist in heat transfer within a portable computer comprising thermally coupling at least one heat generating component of the portable computer to the at least one heat generating component. The battery cell may then be coupled to a cooling assembly. The cooling assembly may be used to direct airflow across at least one radiating wall of the battery cell, wherein the at least one radiating wall of the battery cell has an enhanced surface area. The battery cell may be enclosed in a shield that protects the battery cell from direct heat radiation. The battery cell may be coupled to the motherboard of the portable computer, wherein coupling the battery cell includes using at least one clip. The battery cell may also be detached from the motherboard. The method may further include for charging the battery cells (preferentially) when cooling is required. 
     The method may further comprise including the battery cell in a plurality of battery cells distributed within a portable computer housing and individually, thermally coupled to the at least one heat generating component. In addition, the method may also include maintaining the temperature difference between each battery cell to within a difference of at least less than 10° C. or at least be less than 2° C. The method may also allow for maintaining the capacity difference between each cell to within a difference of at least less than 60 mAH. 
     The method may further comprise individually enclosing the plurality of battery cells in a shield configured to protect a respective battery cell from direct heat radiation. The method may also include coupling the plurality of battery cells to a motherboard of the portable computer or configuring the plurality of cells for detachment. The method may further comprise regulating processing speeds of the portable computer based on the temperature of the at least one heat generating component. 
     In the embedded design, the battery charging process, which is an endothermic (heat absorbing) process, may be coordinated with by using a method to control the thermal management of the computer. To do so, an algorithm can be employed to optimize the charging process to coordinate with a major heat source inside a portable computer, for example CPU or GPU chips. An example for the algorithm is shown in  FIG. 6  for CPU cooling. 
     When the notebook computer is plugged in at  603  with an AC adaptor, the user may select  609  a charge profile either to charge the cells to a full charge (normal mode)  611 , or allow a smart module to control the charge (charge cooling mode) at  613 . Under the second alternative, when the electronics detect that the temperature of the CPU is over the pre-set limit (overheated) at  615 , it will start the charging process at  619  to cool the CPU down by lowering the temperature of the battery (which operates at a lower temperature during charging). In addition, the module can also generate a buffer charging zone when the CPU temperature is low. In this case, the electronics switch to battery power until the state of charge (SOC) of the battery is below or equal to a pre-determined value (low voltage (LV) of SOC) even though the AC adaptor is plugged in, when it detects that the CPU temperature is low. In this way, the battery may be charged when it is needed to increase heat dissipation. The LV and high voltage (HV) may be set, for example, anywhere from 20% to 90% of SOC, preferably 40% to 80%. 
     If the AC adapter is not plugged in at  603 , the portable computer is maintained in normal power mode  607 . If the AC adapter is plugged in at  603 , the user may select battery cooling at  609 . If the user does not select battery cooling  609 , the portable computer may be placed in normal charge mode  611 . If the user selects battery cooling at  609 , the algorithm may then approximate whether the SOC of the battery is greater than LV at  613 , and the algorithm may approximate whether the CPU has overheated at  615 . If the CPU has not overheated at  615 , the portable computer may be powered at  617  using the battery until the LV of SOC has been reached. If the CPU has overheated at  615 , the portable computer may be placed in normal power mode at  619 . If the SOC is not greater than LV at  613 , the portable computer may be placed in normal charge mode until LV of SOC has been reached at  621 . The algorithm may then approximate if the CPU has overheated  623 . If the CPU has not overheated at  623 , the portable computer may be placed in normal power mode at  625 . If the CPU has overheated at  623 , the algorithm may decide to charge the battery to HV at  627 , and the algorithm may repeat the approximation of whether the SOC is greater than LV at  613 . 
     The portable computer may also include a plurality of cells contained within a battery cell pack housing and coupled to the at least one heat generating component. 
     The battery cell pack housing may be located under the palm rest of the portable computer. 
     In another embodiment, the invention includes battery pack  710 , an exploded view of which is shown in  FIG. 7 . Battery pack  710  includes battery cell arrangement  712  of battery cells  714 , electrically connected to circuit  716  by metal strip  718 . Case  720   a,b  of battery pack  710  defines compartment  722  that is in fluid communication with metal strip  718 . Heat pipe  724  is located within compartment  722  and is in direct contact with battery casing  726  of at least one battery cell  714  of battery cell arrangement  712 . The battery casing  726  encloses the battery cell arrangement  712  and functions as a shield that protects the battery cell  714  from direct heat radiation. Alternatively, heat pipe  724  is in direct contact with metal strip  718 . Heat pipe  724  is connected to a heat pipe (not shown) extending to a source of heat within a notebook much as a CPU or GPU. It is to be noted that heat pipe  724  is otherwise electrically insulated from other circuitry of the notebook. Examples of suitable materials of heat pipe  724  include those having a thermal conductivity of at least 7 BTU/(hr ° F. ft 2 /ft). Such examples of preferred materials of heat pipe  724  include aluminum, copper and their alloys, such as alloys of aluminum and copper. 
     In still another embodiment of a battery pack  810 , shown in  FIG. 8 , the battery pack  810  includes a case  820   a,    820   b,  a battery casing  826  with a battery cell arrangement  812  comprised of batteries  814 , a circuit  816 , and a compartment  822 . The battery casing  820   b  defines slot  828  for insertion of a heat pipe (not shown) from the notebook and contact of that heat pipe with another heat pipe, e.g., heat pipe  724  as shown in  FIG. 7 , of battery pack  710 . Otherwise, the battery pack  810  functions in a similar manner as battery pack  710  of  FIG. 7 . 
     Another embodiment of a battery pack  910 , shown in  FIG. 9 , includes a case  920   a,    920   b,  a battery cell arrangement  912 , and a circuit  916 . The battery casing  926  includes a material, at least in part, that provides points of contact between a casing of at least one battery cell  914  of battery cell arrangement  912  and a heat pipe or chassis of the notebook. Examples of suitable materials of battery casing  926  include thermally conductive plastics, such as those well-known in the art, including those that incorporate various fillers, including but not limited to ceramics and carbon fibers, in a resin, including but not limited to polymer, polyamide, poly propylene, polyphenylene sulfide and thermoplastic elastomer. Such materials typically have thermal conductivities greater than about 1 W/mk and up to about 100 W/mk or beyond. Specific examples of suitable polymers include CoolPoly® thermally conductive plastic from Cool Polymers, Inc. of Warwick, R.I.; RTP 199 X 91020 A Z® Thermally Conductive Polypropylene from RTP Company of Winona, Minn.; and Mack TCP® (Thermally Conductive Plastic) from Mack Plastics Corporation of Bristol, R.I. 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 
     Even though embodiments have been shown and described that involve CPUs and GPUs, it should be understood by one with ordinary skill in the art that additional embodiments are available. 
     It should also be understood that the flow diagram of  FIG. 6  is an example that may include more or fewer components, be partitioned into subunits, or be implemented in different combinations.