Patent Publication Number: US-2023155230-A1

Title: Portable power tool, battery pack, and cell configurations for same

Description:
FIELD OF THE INVENTION 
     Various embodiments relate to power tools and battery packs, and more particularly, to twenty volt, lithium ion battery packs and the portable power tools that use them. 
     BACKGROUND OF THE INVENTION 
     Lithium ion battery packs for power tools include several cylindrical, lithium ion battery cells. Each cylindrical cell typically produces 3.6-4.0 volts. More specifically, such cells typically provide 3.6 volts during use and 4.0 volts when fully charged. Marketing departments may label battery packs using such lithium ion cells with voltages between 3.6-4.0 volts or multiples thereof depending on the number of cells in series. Lithium ion battery packs for portable power tools typically include either three lithium ion cells or five lithium ion cells (or multiples thereof in parallel). The three cell packs generally provide 10.8-12.0 volts and are commonly referred to as 12 volt packs. The five cell packs generally provide 18-20 volts are commonly referred to as 20 volt packs. Power tools using the 12 volt packs have the advantage of being lighter and more compact. Conversely, power tools using the 20 volt packs are more powerful. 
     Limitations and disadvantages of conventional and traditional approaches should become apparent to one of skill in the art, through comparison of such systems with aspects of the present invention as set forth in the remainder of the present application. 
     BRIEF SUMMARY OF THE INVENTION 
     Power tools and various lithium ion battery packs for such power tools are substantially shown in and/or described in connection with at least one of the figures, and are set forth more completely in the claims. 
     These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIGS.  1 A- 1 C  show a power tool system that includes a power tool, a battery pack, and battery charger in accordance with an embodiment of the present invention. 
         FIGS.  2 A- 2 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  3 A- 3 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  4 A- 4 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  5 A- 5 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  6 A- 6 D  show a power tool system that includes a power tool and a battery back in accordance with an embodiment of the present invention. 
         FIGS.  7 A- 7 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  8 A- 8 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  9 A- 9 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  10 A- 10 D  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  11 A- 11 E  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  12 A- 12 C  show a power tool system that includes a power tool and a battery pack in accordance with an embodiment of the present invention. 
         FIGS.  13 A and  13 B  show battery cell arrangements in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Aspects of the present invention are related to power tools and battery packs used by such tools. More specifically, certain embodiments of the present invention relate to power tools that may use battery packs having a variety of different forms, cell configurations, and power capabilities. Thus, a power tool vendor may provide a variety of different battery packs in order to permit greater flexibility in matching power, size, weight, etc. of the battery pack to the job at hand. For some jobs, a customer may desire or need greater power. For other jobs, the customer may be willing to sacrifice some power or battery life in order to have a smaller, lighter, better balanced, and/or maneuverable power tool. 
     The figures of the present application generally depict a power tool in the form of a drill driver. Such depiction of a drill driver is for illustrative purposes. The various disclosed battery packs and cell configurations may be utilized with other types of power tools such as, for example impact wrenches, circular saw, miter saws, impact drivers, etc. to name a few. 
       FIGS.  1 A and  1 B  shows a power tool system comprising a power tool  10  and a battery pack  20 . In particular,  FIG.  1 A  depicts the battery pack  20  attached to the power tool  10  and  FIG.  1 B  depicts the battery pack  20  detached from the power tool  10 .  FIG.  1 C  further shows a charger  50  of the power tool system, which may be used to recharge battery cells of the battery pack  20 . 
     As shown in  FIGS.  1 A and  1 B , the power tool  10  may include a handle  11  providing a battery compartment configured to receive the battery pack  20 . More specifically, the handle  11  may include a cavity  12  configured to receive a post portion  22  of the battery pack  20 . The post portion  22  may be inserted into a proximal end of the cavity  12 . The post portion  22  may slide longitudinally into the cavity  12  of the handle  11  and toward a distal end of the cavity  12  until properly seated and attached to power tool  10 . 
     The post portion  22  may include electrical contacts (not shown) that are configured to electrically couple to electrical contacts of the power tool  10  when the post portion  22  is inserted and seated in the cavity  12 . In particular, electrical contacts of the power tool  10  and battery pack  20  may electrically couple rechargeable, battery cells of the battery pack  20  to components (e.g., motor, controller, etc.,) of the power tool  10  so as to provide such components with electrical power when the battery pack  20  is attached to the power tool  10 . 
     The battery pack  20  may further include locking or latching devices which are configured to mechanically, and selectively couple or latch the battery pack  20  to the power tool  10 . In particular, left and right sides of the base portion  24  may each include spring-loaded detents and corresponding release buttons. The detents may engage corresponding recesses or catches of the power tool  10  and secure the battery pack  20  to the power tool  10 . When pressed, the release buttons may actuate correspond detents and cause such detents to disengage the recesses, thus permitting the battery pack  20  to be disengaged and removed from the power tool  10 . 
       FIG.  1 C  depicts a battery charger  50  with a cavity  52  configured to receive the post portion  22  of the battery pack  20 . The battery charger  50  is configured to charge the one or more rechargeable, battery cells of the battery pack  20  when the post portion  22  is inserted in cavity  52  and the post battery  20  is properly seated in the battery charger  50 . The battery charger  50  may include electrical contacts (not shown) that engage the electrical contacts of the battery pack  20  when the post portion  22  is properly inserted and seated in the cavity  52 . In this manner, the battery charger  50  may supply the one or more rechargeable, battery cells with electrical power used to recharge such cells. 
     As shown in  FIG.  1 A , the battery pack  20  may include an outer housing or casing that comprises the post portion  22  and a base or boot portion  24 . The post portion  22  and base portion  24  generally house a plurality of cylindrical, lithium ion battery cells that supply power to the power tool  10  during use. As explained in more detail below, the post portion  22  in various embodiments may include one or more battery cells. Due to housing one or more battery cells in the post portion  22 , all or at least a portion of such cells are positioned within the handle  11  of the power tool  10  when the battery pack  20  is attached to the power tool  10 . Such a configuration reduces the size of the base portion  24  in comparison to a configuration in which all battery cells of the battery pack are housed within the base portion  24 . Moreover, by positioning one or more battery cells in the post portion  22 , the overall size or footprint of the power tool  10  with attached battery pack  20  is also reduced since the portion of the battery pack  20  extending from the power tool  10  (e.g., the base portion  24 ) is smaller. Accordingly, such a power tool  10  with attached battery pack  20  may be easier to maneuver and use than a power tool in which the battery cells are housed solely in a base portion of the attached battery pack. 
     Referring now to  FIGS.  2 A- 2 D,  3 A- 3 D, and  4 A- 4 D , an example power tool  100  is shown in relation to three different twenty volt (20 V) battery packs  200 ,  300 ,  400 . More specifically, the 20 V battery pack  200  of  FIGS.  2 A- 2 D  includes five cylindrical, lithium ion batteries  210  having a diameter of fourteen millimeters (14 mm). The 20 V battery pack  300  of  FIGS.  3 A- 3 D  includes five cylindrical, lithium ion batteries  310  having a diameter of eighteen millimeters (18 mm). The 20 V battery pack  400  of  FIGS.  4 A- 4 D  includes five cylindrical, lithium ion batteries  310  having a diameter of twenty millimeters (20 mm) to twenty-one millimeters (21 mm), hereinafter referred to as 20 mm cells. 
     In comparison to the 18 mm cells  310  and 20 mm cells  410 , the 14 mm cells  210  are compact and light. As such, battery pack  200  is smaller and lighter than the 18 mm cell, battery pack  300  and the 20 mm cell, battery pack  400 . The 14 mm cells  210 , however, are not as powerful as the 18 mm cells  310  or the 20 mm cells. As such, the 14 mm battery pack  200  is generally suitable for jobs where lighter weight, greater maneuverability, and/or smaller size are preferred over greater power and/or longer battery life. 
     The 20 mm cells  410  are larger and heavier than the 14 mm cells  210  and the 18 mm cells  310 . However, as a result of the larger size and greater weight, the 20 mm cells  410  also provide more power than the 14 mm cells  210  and the 18 mm cells  310 . As such, the 20 mm cell, battery pack  400  is generally better suited for jobs where greater power and/or longer battery life is more important than size or weight. 
     The 18 mm cells  310  generally have a lower price point than either the 14 mm cells  210  and the 20 mm cells  410  due to 18 mm cells  310  being extremely prevalent resulting in a much higher manufacturing volume than the 14 mm cells  210  or the 20 mm cells  410 . The 18 mm cells  310  generally provide a performance level between the 14 mm cells  210  and the 20 mm cells  410 . 
     The power tool system of  FIGS.  2 A- 2 D,  3 A- 3 D, and  4 A- 4 D  includes a power tool  100  configured to receive and use any of the battery packs  200 ,  300 ,  400 . In one embodiment, the battery packs  200 ,  300 ,  400  each provide a similarly sized and shaped post portion  220 ,  320 ,  420  for insertion into the handle  110  of the power tool  100 . However, in other embodiments, each of the battery packs  200 ,  300 ,  400  may have a different shape and/or size and a battery compartment of the power tool  100  may be configured to adapt to and/or operably receive each of the different shaped/sized post portions  220 ,  320 ,  420 . Regardless, the power tool  100 , due to its compatibility with each of the battery packs  200 ,  300 ,  400 , may enjoy the unique, benefits provided by each cell size. For example, the power tool  100  may use the smaller, lighter weight battery pack  200  for light duty jobs, use the larger, heavier, and generally more expensive battery pack  400  for heavy duty jobs, and may use the cheaper, all-purpose battery pack  300  when neither light weight nor more power are paramount. 
     Referring now to  FIGS.  2 A- 2 D , further details of the battery pack  200  with respect to power tool  100  will be explained. As shown, the battery pack  200  includes an outer housing  202  or casing having a post portion  220  and a base portion  230 . Similar to the power tool  10  of  FIGS.  1 A and  1 B , the power tool  100  may include a handle  110  providing a battery compartment configured to receive the battery pack  200 . More specifically, the handle  110  may include a cavity configured to receive the post portion  220  of the battery pack  200 . The post portion  220  may be inserted and slid into a proximal end of the cavity toward a distal end of the cavity until the battery pack  200  is properly seated and attached to power tool  100 . 
     The post portion  220  may include electrical contacts (not shown) that are configured to electrically couple to electrical contacts of the power tool  100  when the post portion  220  is inserted and seated in the handle  110  of the power tool  100 . In particular, electrical contacts of the power tool  100  and battery pack  200  may electrically couple rechargeable, battery cells  210  of the battery pack  200  to the power tool  100  so as to provide electrical power to electrical components of the power tool  100 . 
     As shown in  FIGS.  2 C and  2 D , the battery pack  200  includes five battery cells  210  in the housing  202 . In particular, each battery cell  210  may nominally provide 4 volts and may be coupled in series with one another to realize a battery pack  200  that provides a nominal voltage of 20 volts. The battery cells  210  may be any rechargeable battery cell chemistry type, such as, for example, nickel cadmium (NiCd), nickel-metal hydride (NiMH), Lithium (Li), Lithium-ion (Li-ion), other Lithium-based chemistry, other rechargeable battery cell chemistry, etc. However, in one preferred embodiment, each of the battery cells  210  is a lithium-ion battery cell. 
     As shown, each battery cell  210  may have generally cylindrical shape and may extend along a cell axis  242 ,  252  that is parallel to an outer, cylindrical cell wall of each cell  210 . Moreover, each battery cell  210  may have a diameter of about fourteen millimeters (14 mm) and a length in the range of about sixty millimeters (60 mm) to about seventy millimeters (70 mm), with nominal lengths of 60 mm, 65 mm, and 70 mm preferred in some embodiments. 
     As shown, the battery cells  210  are arranged in a first group  240  of three battery cells and a second group  250  of two battery cells. In the first group  240 , the cell axes  242  are parallel to one another. In the second group  250 , the cell axes  252  are parallel to each other. However, the first group  240  and the second group  250  are arranged so that the cell axes  242  of the first group  240  are not parallel to the cell axes  252  of the second group  250 . As shown in  FIG.  2 D , the cell axes  242  of the first group  240  may be perpendicular or nearly perpendicular (e.g., 90°±5°) to the cell axes  252  of the second group  252 . However, in other embodiment, the cell axes  242  of the first group  240  may form a more acute angle (e.g., between about 90° and about 70°, or between about 90° and about 45°) with the cell axes  252  of the second group  250 . 
     Moreover, the first group  240  of cells  210  are positioned to correspond to the post portion  220  of the battery pack housing  202  and the second group  250  of cells  210  are positioned to correspond to the base portion  230  of the battery pack housing  202 . As a result of such configuration, the first group  240  of cells  210  are generally received by the handle  110  of the power tool  100  when the battery pack  200  is attached to the power tool  100 . Conversely, the second group  250  of cells  210  are generally not received by the handle  110  of the power tool  100  when the battery pack  200  is attached to the power tool. 
     In some embodiments, the first group  240  of cells  210  are completely received by the power tool  100  or handle  110  such that 100% of the volume of each cell  210  in the first group  240  is contained within the power tool  100  or handle  110 . In other embodiments, the first group  240  is substantially received by the handle  110  such that greater than 80% of the volume of each cell  210  is contained within the power tool  100  or handle  110  and less the 20% of the volume of each cell  210  extends beyond the power tool  100  or handle  110 . In yet other embodiments, the first group  240  is mostly received by the power tool  100  or handle  110  such that greater than 50% of the volume of each cell  210  is contained within the power tool  100  or handle  110  and less the 50% of the volume of each cell  210  extends beyond the power tool  100  or handle  110 . 
     By arranging the battery cells  210  in the battery pack  200  such that one or more cells  210  extend into the power tool  100  or handle  110  when attached, the battery pack  200  reduces the overall size or footprint of the power tool  100  when in use. More specifically, a battery pack such as battery pack  200  reduces the usable footprint of the power tool  100  when compared to a battery pack in which none of the cells are contained, substantially contained, or mostly contained by the power tool  100  or handle  110  when the battery pack is attached to the power tool  100 . 
     Referring now to  FIGS.  3 A- 3 D , further details of the battery pack  300  with respect to power tool  100  will be explained. As shown, the battery pack  300  includes an outer housing  302  or casing having a post portion  320  and a base portion  330 . Similar to the post portion  220  of battery pack  200 , the post portion  320  may be inserted and slid into a proximal end of a power tool cavity toward a distal end of the cavity until the battery pack  300  is properly seated and attached to power tool  100 . 
     The post portion  320  may include electrical contacts (not shown) that are configured to electrically couple to electrical contacts of the power tool  100  when the post portion  320  is inserted and seated in the handle  110  of the power tool  100 . In particular, electrical contacts of the power tool  100  and battery pack  300  may electrically couple rechargeable, battery cells  310  of the battery pack  300  to the power tool  100  so as to provide electrical power to electrical components of the power tool  100 . 
     As shown in  FIGS.  3 C and  3 D , the battery pack  300  includes five battery cells  310  in the housing  302 . In particular, each battery cell  310  may nominally provide 4 volts and may be coupled in series with one another to realize a battery pack  300  that provides a nominal voltage of 20 volts. The battery cells  310  may be any rechargeable battery cell chemistry type, such as, for example, nickel cadmium (NiCd), nickel-metal hydride (NiMH), Lithium (Li), Lithium-ion (Li-ion), other Lithium-based chemistry, other rechargeable battery cell chemistry, etc. However, in one preferred embodiment, each of the battery cells  310  is a lithium-ion battery cell. 
     As shown, each battery cell  310  may have generally cylindrical shape and may extend along a cell axis  342 ,  352  that is parallel to an outer, cylindrical cell wall of each cell  310 . Moreover, each battery cell  310  may have a diameter of about eighteen millimeters (18 mm) and a length in the range of about sixty millimeters (60 mm) to about seventy millimeters (70 mm), with nominal lengths of 60 mm, 65 mm, and 70 mm preferred in some embodiments. 
     As shown, the battery cells  310  are arranged in a first group  340  of two battery cells and a second group  350  of three battery cells. In the first group  340 , the cell axes  342  are parallel to one another. In the second group  350 , the cell axes  352  are parallel to each other. However, the first group  340  and the second group  350  are arranged so that the cell axes  342  of the first group  340  are not parallel to the cell axes  352  of the second group  350 . As shown in  FIG.  3 D , the cell axes  342  of the first group  340  may be perpendicular or nearly perpendicular (e.g., 90°±5°) to the cell axes  352  of the second group  352 . However, in other embodiments, the cell axes  342  of the first group  340  may form a more acute angle (e.g., between about 90° and about 70°, or between about 90° and about 45°) with the cell axes  352  of the second group  350 . 
     Moreover, the first group  340  of cells  310  are positioned to correspond to the post portion  320  of the battery pack housing  302  and the second group  350  of cells  310  are positioned to correspond to the base portion  330  of the battery pack housing  302 . As a result of such configuration, the first group  340  of cells  310  are generally received by the handle  110  of the power tool  100  when the battery pack  300  is attached to the power tool  100 . Conversely, the second group  350  of cells  310  are generally not received by the handle  110  of the power tool  100  when the battery pack  300  is attached to the power tool. 
     In some embodiments, the first group  340  of cells  310  are completely received by the power tool  100  or handle  110  such that 100% of the volume of each cell  310  in the first group  340  is contained within the power tool  100  or handle  110 . In other embodiments, the first group  340  is substantially received by the handle  110  such that greater than 80% of the volume of each cell  310  is contained within the power tool  100  or handle  110  and less the 20% of the volume of each cell  310  extends beyond the power tool  100  or handle  110 . In yet other embodiments, the first group  340  is mostly received by the power tool  100  or handle  110  such that greater than 50% of the volume of each cell  310  is contained within the power tool  100  or handle  110  and less the 50% of the volume of each cell  310  extends beyond the power tool  100  or handle  110 . 
     By arranging the battery cells  310  in the battery pack  300  such that one or more cells  310  extend into the power tool  100  or handle  110  when attached, the battery pack  300  reduces the overall size or footprint of the power tool  100  when in use. More specifically, a battery pack such as battery pack  300  reduces the usable footprint of the power tool  100  when compared to a battery pack in which none of the cells are contained, substantially contained, or mostly contained by the power tool  100  or handle  110  when the battery pack is attached to the power tool  100 . 
     Referring now to  FIGS.  4 A- 4 D , further details of the battery pack  400  with respect to power tool  100  will be explained. As shown, the battery pack  400  includes an outer housing  402  or casing having a post portion  420  and a base portion  430 . Similar to the post portion  220  of battery pack  200 , the post portion  420  may be inserted and slid into a proximal end of a power tool cavity toward a distal end of the cavity until the battery pack  400  is properly seated and attached to power tool  100 . 
     The post portion  420  may include electrical contacts (not shown) that are configured to electrically couple to electrical contacts of the power tool  100  when the post portion  420  is inserted and seated in the handle  110  of the power tool  100 . In particular, electrical contacts of the power tool  100  and battery pack  400  may electrically couple rechargeable, battery cells  410  of the battery pack  400  to the power tool  100  so as to provide electrical power to electrical components of the power tool  100 . 
     As shown in  FIGS.  4 C and  4 D , the battery pack  400  includes five battery cells  410  in the housing  402 . In particular, each battery cell  410  may nominally provide 4 volts and may be coupled in series with one another to realize a battery pack  400  that provides a nominal voltage of 20 volts. The battery cells  410  may be any rechargeable battery cell chemistry type, such as, for example, nickel cadmium (NiCd), nickel-metal hydride (NiMH), Lithium (Li), Lithium-ion (Li-ion), other Lithium-based chemistry, other rechargeable battery cell chemistry, etc. However, in one preferred embodiment, each of the battery cells  410  is a lithium-ion battery cell. 
     As shown, each battery cell  410  may have generally cylindrical shape and may extend along a cell axis  442 ,  452  that is parallel to an outer, cylindrical cell wall of each cell  410 . Moreover, each battery cell  410  may have a diameter of about twenty millimeters (20 mm) and a length in the range of about sixty millimeters (60 mm) to about seventy millimeters (70 mm), with nominal lengths of 60 mm, 65 mm, and 70 mm preferred in some embodiments. 
     As shown, the battery cells  410  are arranged in a first group  440  of two battery cells and a second group  450  of three battery cells. In the first group  440 , the cell axes  442  are parallel to one another. In the second group  450 , the cell axes  452  are parallel to each other. However, the first group  440  and the second group  450  are arranged so that the cell axes  442  of the first group  440  are not parallel to the cell axes  452  of the second group  450 . As shown in  FIG.  4 D , the cell axes  442  of the first group  440  may be perpendicular or nearly perpendicular (e.g., 90°±5°) to the cell axes  452  of the second group  452 . However, in other embodiments, the cell axes  442  of the first group  440  may form a more acute angle (e.g., between about 90° and about 70°, or between about 90° and about 45°) with the cell axes  452  of the second group  450 . 
     Moreover, the first group  440  of cells  410  are positioned to correspond to the post portion  420  of the battery pack housing  402  and the second group  450  of cells  410  are positioned to correspond to the base portion  430  of the battery pack housing  402 . As a result of such configuration, the first group  440  of cells  410  are generally received by the handle  110  of the power tool  100  when the battery pack  400  is attached to the power tool  100 . Conversely, the second group  450  of cells  410  are generally not received by the handle  110  of the power tool  100  when the battery pack  400  is attached to the power tool. 
     In some embodiments, the first group  440  of cells  410  are completely received by the power tool  100  or handle  110  such that 100% of the volume of each cell  210  in the first group  240  is contained within the power tool  100  or handle  110 . In other embodiments, the first group  440  is substantially received by the handle  110  such that greater than 80% of the volume of each cell  410  is contained within the power tool  100  or handle  110  and less the 20% of the volume of each cell  410  extends beyond the power tool  100  or handle  110 . In yet other embodiments, the first group  440  is mostly received by the power tool  100  or handle  110  such that greater than 50% of the volume of each cell  410  is contained within the power tool  100  or handle  110  and less the 50% of the volume of each cell  410  extends beyond the power tool  100  or handle  110 . 
     By arranging the battery cells  410  in the battery pack  400  such that one or more cells  410  extend into the power tool  100  or handle  110  when attached, the battery pack  400  reduces the overall size or footprint of the power tool  100  when in use. More specifically, a battery pack such as battery pack  400  reduces the usable footprint of the power tool  100  when compared to a battery pack in which none of the cells are contained, substantially contained, or mostly contained by the power tool  100  or handle  110  when the battery pack is attached to the power tool  100 . 
     Referring now to  FIGS.  5 A- 5 D , further details of another power tool system comprising a power tool  100 ′ and a battery pack  500 . The power tool system is similar to the power tool system of  FIGS.  2 A- 2 D,  3 A- 3 D, and  4 A- 4 D . However, the battery cells  510  of battery pack  500  are stacked in a longitudinal manner. Namely, the battery pack  500  like battery packs  200 ,  300 ,  400  includes a first group  540  of battery cells and a second group  550  of battery cells. However, the first group  540  is shown having a single battery cell  510  and the second group  550  is shown as having four battery cells  510 . Moreover, the cells  510  of the first group  540  are stacked longitudinally upon the cells  510  of the second group  550  such that the cell axes  542 ,  552  of each group  540 ,  550  are parallel or nominally parallel (e.g., ±5°) to one another. 
     Moreover, the first group  540  of cells  510  are positioned to correspond to a post portion  520  of the battery pack housing  502  and the second group  550  of cells  410  are positioned to primarily correspond to the base portion  530  of the battery pack housing  502 . However, as depicted, the second group  550  of cells  510  may significantly extend into the post portion  520  as well. As a result of such an arrangement, the first group  540  of cells  510  are generally received by the handle  110  of the power tool  100  when the battery pack  400  is attached to the power tool  100 . Moreover, at least a significant portion of the second group  450  of cells  410  are also received by the handle  110  of the power tool  100  when the battery pack  400  is attached to the power tool. 
     In some embodiments, the first group  540  of cells  510  is completely received by the power tool  100  or handle  110  such that 100% of the volume of each cell  510  in the first group  540  is contained within the power tool  100  or handle  110 . Moreover, the second group  540  is significantly received by the handle  110  such that greater than 20% of the volume of each cell  510  is contained within the power tool  100  or handle  110 . In yet other embodiments, the second group  550  is mostly received by the power tool  100  or handle  110  such that greater than 50% of the volume of each cell  510  is contained within the power tool  100  or handle  110  and less the 50% of the volume of each cell  510  of the second group  550  extends beyond the power tool  100  or handle  110 . 
     Referring now to  FIGS.  6 A- 6 D , further details of another power tool system comprising a power tool  100 ″ and a battery pack  600 . The power tool system is similar to the power tool system of  FIGS.  2 A- 2 D,  3 A- 3 D, and  4 A- 4 D . However, the battery cells  610  in the base portion  630  are stacked like logs. Namely, the battery pack  600  like battery packs  200 ,  300 ,  400  includes a first group  640  of battery cells and a second group  550  of battery cells. However, the cells  610  of the second group  650  are stacked such that the cylindrical walls of at least one of the battery cells  610  rests upon the cylindrical walls or is positioned above the cylindrical walls of another battery cell  610  of the second group  650 . 
     The first group  640  of cells  510  are positioned to correspond to a post portion  620  of the battery pack housing  602  and the second group  650  of cells  610  are positioned to primarily correspond to the base portion  630  of the battery pack housing  602 . Similar to battery packs  200 ,  300 , and  400 , the first group  640  of cells  410  may be completely received, may be substantially received, or may be mostly received by the power tool  100  or handle  110  such that 100%, greater than 80%, or greater than 50% of the volume of each cell  610  in the first group  640  is contained within the power tool  100  or handle  110 . 
     Referring now to  FIGS.  7 A- 7 D , further details of another power tool system comprising a power tool  100 ″′ and a battery pack  700 . The power tool system is similar to the power tool system of  FIGS.  2 A- 2 D,  3 A- 3 D, and  4 A- 4 D . However, the battery cells  710  in the base portion  730  are spread apart to permit battery cells in the post portion  720  to extend into the base portion  730 . Namely, the battery pack  700  like battery packs  200 ,  300 ,  400  includes a first group  740  of battery cells and a second group  750  of battery cells. However, two of the cells  710   a,    710   b  from the second group  750  are laterally separated from each other such that a gap  754  is formed between the cylindrical walls of the two cells  710   a,    710   b  while the cell axes  752   a,    752   b  of the two cells  710   a,    710   b  remain parallel to each other. Furthermore, the third cell  710   c  is positioned such that the cell axis  752   c  of the third cell  710   c  is perpendicular to, but lies in the same plane as the cell axes  752   a,    752   b  of the two cells  710   a,    710   b.  Such an arrangement, permits distal end of the cells  710   d,    710   e  of the first group  740  to extend into the gap  754  between the cells  710   a,    710   b,  thus reducing the overall height of the battery pack  700 . Moreover, such an arrangement results in the cell axes  742   d,    742   e  being perpendicular or nearly perpendicular with the cell axes  752   a,    752   b,    752   c.  In some embodiments, the cell axes  742   d,    742   e  may form a more acute angle with the cell axes  752   a,    752   b,    752   c.    
     Referring now to  FIGS.  8 A- 8 D , further details of another 20 V battery pack  800  for use with the power tool system of  FIGS.  2 A- 2 D,  3 A- 3 D, and  4 A- 4 D . Unlike the packs  200 ,  300 ,  400 , the battery pack  800  includes ten battery cells  810  instead five battery cells. In particular, the first group  840  associated with the post portion  820  of the housing  802  includes two battery cells  810 , but the second group  850  associated with the base portion  830  of the housing includes eight battery cells  810 . The cell axes  842  of the first group  840  are perpendicular or nearly perpendicular to the cell axes  852  of the second group  850 . However, the cells  810  of the second group  850  are arranged such that a first layer  856  of four cells  810  are stacked such that their cylindrical walls are in close proximity (e.g., about 0.030 inches apart) to the cylindrical walls of a second layer  858  of cells  810 . Moreover, the cell axes  852  are rotated with respect to the cell axes of packs  200 ,  300 ,  400  such that the cell axes  852  align with a line extending from a left and right side of the power tool  100  instead of aligning with a line extending from a front and back side of the power tool  100 . 
       FIGS.  8 A- 8 D  depict the battery pack  800  with ten battery cells  810 . However, a similar technique may be utilized to extend the battery pack  800  to other multiples of five such as fifteen battery cells. For example, a third layer of five battery cells  810  could be arranged under second layer  858 . 
       FIGS.  9 A- 9 D  show that the battery packs  200 ,  300 ,  400 ,  500 ,  600 ,  700 ,  800  may be implemented such that the packs may be inserted into the power tool  100  in at least two orientations. However, embodiments that permit insertion of the battery packs in a greater number of orientations are envisioned and contemplated. 
     As shown in  FIGS.  9 A and  9 B , the base or boot portion  930  of a battery pack  900  may extend further to a front of the power tool  100  than toward a back of the power tool  100 . As such, the battery pack  900  in the orientation of  FIGS.  9 A and  9 B  presents more weight toward the front of the power tool  100  than the back of the power tool  100 . As shown in  FIGS.  9 C and  9 D , the battery pack  900  inserted into the power tool  100  such that the pack  900  extends further toward the back of the power tool  100  than the front of the power tool  100 . Such an orientation may better balance the power tool  100  along the handle  110  making the power tool  100  easier to use. Furthermore, such rotation adjusts the foot print or silhouette of the power tool  100  during use. When used in tight quarters, reorienting the battery pack  900  may provide additional clearance enabling the use of the power tool  900  in a small area that may not otherwise be accessible or may be more difficult to access if the battery pack  900  were not reoriented. 
     Referring now to  FIGS.  10 A- 10 D , another embodiment of a power tool system is shown in which a first portion  1012  of the handle  1010  for the power tool  1000  is provided by the power tool  1000  and a second portion  1014  of the handle  1010  is provided by the battery pack  1100 . The battery pack  1100  may be implemented in a manner similar to the previously discussed battery packs. However, the housing  1102  of the battery pack  1100  may incorporate the second portion  1014  of the handle  1010  into the post portion  1120  of the battery pack  1100 . The battery pack  1100  may enable the power tool  1000  to have a smaller handle  1010  since the handle  1010  no longer needs to provide clearance for receiving the post portion  1120  of the battery pack  1100 . For example, in the embodiment of  FIGS.  10 A- 10 D , the handle  1010  may provide clearance for the receipt of a front surface  1122  of the post portion. However, since the second portion  1014  is incorporated into the post portion  1122 , the post portion  1120  does not have a corresponding rear surface to be received, thus permitting the handle  1010  to be smaller than otherwise would be permitted. 
     Referring now to  FIGS.  11 A- 11 E , another embodiment of a power tool system is shown in which two battery cells  1210  are incorporated into the handle  1310  of the 20 V power tool  1300 . As a result of incorporating two battery cells  1210  into the handle  1310 , the handle  1310  does not need to receive a post portion from battery pack. As such, the handle  1310  may be implemented to be smaller than the handles  110  of the above-described power tool  100 . As shown, the power tool  1300  may instead user a smaller battery pack  1200  which includes three battery cells  1210  having cell axes  1252  roughly perpendicular to cell axes  1242  of the battery cells  1210  incorporated into the handle  1310 . Furthermore, the battery pack  1200  may include a slide portion  1220  which may engage rails  1330  of the power tool  1300 . 
     Referring now to  FIGS.  12 A- 12 C , yet another embodiment of a power tool system similar to the power tool system of  FIGS.  11 A- 11 E  is shown. Like the power tool system of  FIGS.  11 A- 11 E , the 20 V power tool  1400  of  FIGS.  12 A- 12 C  may incorporate one or more battery cells (not shown) into its handle  1410 . The battery pack  1500  may include a slide portion  1520  similar to the slide portion  1320  of battery pack  1300 . However, unlike the battery pack  1200  which utilizes three cylindrical, lithium-ion battery cells  1210 , the battery pack  1500  may include one or more lithium polymer battery cells  1510 . In another embodiment, the lithium polymer battery cells  1510  may provide twenty volts on their own, thus permitting embodiments without additional battery cells in the handle  1410 . 
     While the above battery packs were described as using battery cells having a single size (e.g., 14 mm, 18 mm, or 20 mm), some battery packs may utilize battery cells of more than one size. Mixing battery cells of different sizes may reduce the volume of consumed by the battery cells of the battery pack and may help provide a denser design. For example, the right side of  FIG.  13 A  illustrates an arrangement of ten battery cells using a single size (e.g., 18 mm lithium-ion cells). The left side of  FIG.  13 A  presents a similar arrangement of ten battery cells but utilizes a mix of cell sizes (e.g., 20 mm and 14 mm lithium-ion cells). The arrangement of ten cells of the left side may be capable of delivering similar performance as the arrangement of ten cells on the right side. However, as depicted, the arrangement of ten cells on the left side has a reduced vertical height in comparison to the ten cells on the right side. 
       FIG.  13 B  depicts yet another arrangement of ten cells of mixed sizes (e.g., 20 mm and 14 mm lithium-ion cells). Again, the arrangement of ten cells shown in FIG.  13 B may be capable of delivering similar performance as the arrangements shown in  FIG.  13 A . However, the arrangement of  FIG.  13    consumes a smaller volume than either arrangement of  FIG.  13 A . 
     In some embodiments, the battery packs may include circuitry to monitor battery characteristics, to provide voltage detection, to store battery characteristics, to display battery characteristics, to inform a user of certain battery characteristics, to suspend current within the battery pack, to detect temperature of the battery pack, battery cells, and the like, to transfer heat from and/or within the battery pack, and to provide balancing methods when an imbalance is detected within one or more battery cells. In some embodiments, such circuitry may include a voltage detection circuit, a boosting circuit, a state of charge indicator, and the like. 
     In some embodiments, the circuitry may also include processing circuitry such as a microprocessor or microcontroller. The processing circuitry may monitor various battery pack parameters (e.g., battery pack present state of charge, battery cell present state of charge, battery pack temperature, battery cell temperature, and the like), may store various battery pack parameters and characteristics (including battery pack nominal voltage, chemistry, and the like, in addition to the parameters), may control various electrical components, and may communicate with other electrical devices, such as, for example, a power tool, a battery charger, and the like. In some embodiments, the processing circuitry may monitor each battery cell&#39;s present state of charge and may identify when an imbalance occurs (e.g., the present state of charge for a battery cell exceeds the average cell state of charge by a certain amount or drops below the average cell state of charge by a certain amount). In some embodiments, the processing circuitry may re-balance the cells when an imbalance has been detected. 
     Various embodiments of the invention have been described herein by way of example and not by way of limitation in the accompanying figures. For clarity of illustration, exemplary elements illustrated in the figures may not necessarily be drawn to scale. In this regard, for example, the dimensions of some of the elements may be exaggerated relative to other elements to provide clarity. Furthermore, where considered appropriate, reference labels have been repeated among the figures to indicate corresponding or analogous elements. 
     While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiment or embodiments disclosed, but that the present invention encompasses all embodiments falling within the scope of the appended claims.