Patent Publication Number: US-9407024-B2

Title: Multidirectional electrical connector, plug and system

Description:
BACKGROUND 
     1. Technical Field 
     The embodiments described herein relate to portable electrical energy storage devices, such as those used to power electric powered devices such as vehicles and consumer electronics, and connectors for making an electrical connection between such portable electrical energy storage devices and devices to be powered by or used to charge such portable electrical energy storage devices. 
     2. Description of the Related Art 
     Batteries such as lithium-ion batteries are known for storing more energy into smaller, lighter units. Lithium-ion batteries have found wide application in powering portable electronic devices such as cell phones, tablets, laptops, power tools and other high-current equipment. The low weight and high energy density also makes lithium-ion batteries attractive for use in hybrid electric vehicles and fully electric-powered vehicles. 
     In some applications, a plurality of individual lithium-ion batteries are packaged together to form a battery pack. Such battery packs include electrical components that make electrical connection between the plurality of individual lithium-ion batteries and primary negative and positive electrical terminals of the battery pack. The negative and positive electrical terminals of the battery pack can be connected to corresponding negative and positive electrical terminals of a device to provide electric power to the device. In applications such as computers or mobile phones, the electric connection to the electrical terminals of the battery pack often can only be achieved when the battery pack is inserted into the battery compartment in one position. In other positions, the battery pack either cannot be received into the battery compartment and/or the terminals of the battery pack do not make electrical connection to the terminals of the device. Similarly, chargers for such types of battery packs often include compartments for receiving the battery pack to be charged. The battery compartment of these chargers is often a replica of the compartment contained in the device to be powered by the battery pack. As with the devices, if the battery pack is not oriented properly in the battery compartment of the battery charger, the battery pack may be not be accepted into the compartment and/or the electrical terminals of the battery pack may not make electrical connection with the electrical terminals of the charger. In other instances, when the battery pack is received into the battery compartment of the charger or device in an improper orientation, the electrical terminals of the battery pack may make contact with the electrical terminals of the charger or the device; however, such contact may not meet the design parameters set for the electrical connection between the battery pack and the charger and/or device. For example, the area of contact between the electrical terminals of the battery pack and the electrical terminals of the device or charger when the battery pack is not in its proper orientation may be less than the area of contact between the electrical terminals of the battery pack and the electrical terminals of the device or charger when the battery pack is in its proper orientation. This reduced area of contact when the battery pack is not in its proper orientation can result in the temperature of the electrical terminals rising to undesired and potentially unsafe levels. 
     Insertion of a battery pack in an improper orientation within a device to be electrically powered by the battery pack or within a device for charging the battery pack may occur due to the user&#39;s lack of understanding the proper orientation or due to carelessness on the part of the user. With the proliferation of electric powered devices, such as electric powered tools, appliances, personal portable communication devices, laptop and tablet computers, personal media devices, vehicles and the like, there is interest in battery pack and battery pack electrical connection designs that minimize the likelihood of installing a battery pack in an orientation within a device to be powered by the battery pack or within a device for charging the battery pack such that the electrical power does not flow between the two or does flow, but creates unsafe conditions. Avoiding improper orientation avoids the risk of creating potentially unsafe conditions and promotes proper discharge and charging of the battery pack, as well as avoiding damage to the terminals of the battery pack and/or terminals of the electrically powered device or charging device. 
     Connectors capable of electrically connecting a source of electrical energy to a device to be powered by electrical energy from the source of electrical energy without regard to the rotational orientation of the connector are known. For example, connectors historically referred to as 12V cigarette lighter socket, utilize a round female connector and a round male connector. An electrical connection can be made between the two, regardless of the rotational orientation the male connector is inserted in the female connector. Such types of connectors are designed for 12V systems and typically have recommended maximum operating currents on the order of 5 to 10 amps, well below current levels required for modern day high current draw devices, e.g., electric powered tools, electric powered appliances and electric powered vehicles, which draw current at levels one or two orders of magnitude greater than current levels 12V cigarette lighter electrical connectors are rated. 
     Even when a battery pack is installed/inserted in a proper orientation, the electrical connection between electrical terminals of the battery pack and electrical terminals of a device to be powered by the battery pack or a device for charging the battery pack may not operate as designed. For example, unwanted conductive or nonconductive materials could become lodged between the terminals of the battery pack and the terminals of the device or charger. Portions of the terminals could become damaged or could be broken off. Such conditions can result in unsafe conditions and degraded performance. Thus, even in situations where the battery pack is installed/inserted in its proper orientation, there is interest in effective ways to confirm the electrical connection between the electrical terminals of the battery pack and the electrical terminals of the electrically powered device or the device for charging the battery is as designed. 
     BRIEF SUMMARY 
     Zero tail pipe emissions alternatives to combustion engines would greatly benefit the air quality of, and hence health of, large populations. 
     While the zero tail pipe emissions benefit of all-electric vehicles are appreciated, adoption of all-electric vehicles by large populations has been slow. One of the reasons appears to be the cost, particularly the cost of secondary batteries. Another one of the reasons appears to be the limited driving range available on a single charge of a battery, and the relatively long time (e.g., multiple hours) necessary to recharge a secondary battery when depleted. Yet another reason appears to be the complicated nature of replacing secondary batteries in all-electric vehicles. 
     The approaches described herein may address some of the issues which have limited adoption of zero tailpipe emission technology, particularly in densely crowded cities, and in populations with limited financial resources. 
     For example, subject matter described herein relates to connectors for electrically connecting portable electrical energy storage devices, e.g., batteries or battery packs, to a device to be powered by the portable electrical energy storage device or a device for charging the portable electrical energy storage device. The connectors can make an electrical connection between the portable electrical energy storage device and a device to be powered by the portable electrical energy storage device or a device for charging the portable electrical energy storage device in more than one spatial (e.g., rotational) orientation. Electrical connectors for portable electrical energy storage devices of the type described herein are able to make the above-described electrical connections in a plurality of spatial orientations (e.g., a first position, a second position rotated from the first position, a third position rotated from the first and second position, and other rotational positions). The described connectors provide safe electrical connection between a portable electrical energy storage device and an electric device having extended time period electrical current that demands one, two or even more orders of magnitude greater than extended time period current ratings for conventional electrical connectors, such as 12V cigarette lighter style electrical connectors which typically have extended time period current ratings from about 5 to 10 amps and momentary peak ratings of about 15 to 20 amps. Conventional electrical connectors like cigarette lighter style electrical connectors include a positive pin in the form of a spring and point contact which are not designed to safely handle currents much greater than 20 amps or applications involving high levels of vibration. Connectors of the type described herein provide an advantage in that robust and safe electrical connections can be made in a plurality of the spatial orientations of the connector on the portable electrical energy storage device relative to the connector on the electrically powered device or the device for charging the portable electrical energy storage device. 
     Because a portable electrical energy storage device connector in accordance with embodiments described herein can mate with a connector of the electrically powered device or the device for charging the portable electrical storage device in a plurality of specific spatial orientations in which the portable electrical energy storage device is installed or received by the electrically powered device or the device for charging the portable electrical energy storage device, users of portable electrical energy storage devices utilizing electrical connectors of the type described herein will be confident that a robust and safe electrical connection can be made to an electrically powered device or a device for charging the portable electrical energy storage device. The user will be less concerned with and less likely to install the portable electrical energy storage device incorrectly and therefore utilization of the portable electrical energy storage devices will be safer and occur more rapidly and be more widespread. 
     Electrical connectors of the type described herein include a connector for making electrical connection between a portable electrical energy storage device electrically connected to the connector or an electric powered device electrically connected to the connector and a plug electrically connected to an electric powered device or a portable electrical energy storage device that is not electrically connected to the connector. The connectors include an electrically nonconductive connector base having a connector central axis; an electrical contact housing including an outer sidewall extending in a direction parallel to the connector central axis and an inner sidewall extending in a direction parallel to the connector central axis, the inner sidewall located closer to the connector central axis than the outer sidewall, the electrical contact housing centered on the connector central axis; a first terminal including at least two electrically conductive contact pads located adjacent the inner sidewall of the electrical contact housing; and a second terminal including at least one electrically conductive contact pad located adjacent the outer sidewall of the electrical contact housing. 
     The connectors may further comprise a connection test terminal located closer to the connector central axis than the first terminal and configured to be electrically connected to the first terminal when the connector is electrically connected to the plug. 
     The connection test terminal may include a high impedance material. 
     The connectors may be configured to mate with the plug in two or more orientations and make an electrical connection to the plug in each of the two or more orientations, the two or more orientations corresponding to different positions of the connector relative to the plug, each different position of the connector relative to the plug corresponding to different rotational positions of the connector relative to the connector central axis. 
     The two or more orientations may be three or more orientations, four or more orientations, or five or more orientations. 
     The electric powered device may be a traction electric motor for a vehicle. 
     The outer sidewall and the inner sidewall of the connector may be concentric. 
     The at least two electrically conductive contact pads of the first terminal and the at least one electrically conductive pad of the second terminal may be concentric. 
     The at least two electrically conductive contact pads may include at least three electrically conductive contact pads. 
     The at least one electrically conductive contact pad of the second terminal may include two or more contact pads. 
     A periphery of the electrical contact housing may lie in a plane perpendicular to the connector central axis and the periphery may define a quadrilateral with opposing angles that are equal. Adjacent sides of the quadrilateral may be equal in length. 
     The outer sidewall of the electrical contact housing may include four outer sidewalls with each outer sidewall arranged perpendicular to adjacent outer sidewalls and extending parallel to the connector central axis. The inner sidewall of the electrical contact housing may include four inner sidewalls with each inner sidewall arranged perpendicular to adjacent inner sidewalls and extending parallel to the connector central axis. The four inner sidewalls may be located closer to a connector base axis than the four outer sidewalls. 
     The at least two electrically conductive contact pads of the first terminal may include four electrically conductive contact pads, and one electrically conductive contact pad of the first terminal may be located adjacent each of the four inner sidewalls of the electrical contact housing. 
     The at least one electrically conductive contact pad of the second terminal may include four electrically conductive contact pads, and one electrically conductive contact pad of the second terminal may be located adjacent each of the four outer sidewalls of the electrical contact housing. 
     An electrical plug for making electrical connection between an electric powered device electrically connected to the plug or a portable electrical energy storage device electrically connected to the plug and a connector electrically connected to an electric powered device or a portable electrical energy storage device that is not electrically connected to the plug may include an electrically nonconductive plug housing including a plug end, a terminal end and a plug housing central axis, the plug end located at an end of the nonconductive plug housing that is opposite an end of the nonconductive plug housing where the terminal end is located; a first terminal located at the plug end and including at least two electrically conductive contact pads, each contact pad of the first terminal extending parallel to the plug housing central axis and positioned around the plug housing central axis; and a second terminal located at the plug end and including at least two electrically conductive contact pads, each contact pad of the second terminal extending parallel to the plug housing central axis and positioned around the plug housing central axis, the first terminal of the plug located closer to the plug housing central axis than the second terminal of the plug, each contact pad of the first terminal separated from the contact pads of the second terminal by an electrically nonconductive medium. 
     The plug may further include a connection test terminal located at the plug end further from the plug housing central axis than the contact pads of the first plug terminal, the connection test terminal configured to be electrically connected to the connector when the connector mates with the plug. 
     The plug may be configured to mate with the connector when the connector is in one of two or more orientations and the plug is configured to make an electrical connection to the connector in each of the two or more orientations with each of the connector&#39;s two or more orientations corresponding to a different position of the connector relative to the plug with each different position of the connector relative to the plug achieved by rotating the connector around the plug housing central axis. 
     The two or more orientations may be three or more orientations, four or more orientations, or five or more orientations. 
     The electric powered device may be a traction electric motor. 
     The at least two contact pads of the first terminal and the contact pads of the second terminal may be concentric. 
     The at least two contact pads of the first terminal may be are three contact pads or may be four contact pads. 
     The at least two contact pads of the second terminal may be three contact pads. 
     A system for electrically connecting a portable electrical energy storage device to an electrically powered device may include a connector that may include an electrically nonconductive connector base including a connector central axis; an electrical contact housing that may include an outer sidewall extending in a direction parallel to the connector central axis and an inner sidewall extending in a direction parallel to the connector central axis, the inner sidewall located closer to the connector central axis than the outer sidewall and the electrical contact housing centered on the connector central axis; a first connector terminal that may include at least one electrically conductive contact surface located adjacent the inner sidewall of the electrical contact housing; and a second connector terminal that may include at least one electrically conductive contact surface located adjacent the outer sidewall of the electrical contact housing. 
     The system may further include a plug including an electrically nonconductive plug housing including a plug end, a terminal end and a plug housing central axis, the plug end may be located at an end of the nonconductive plug housing that is opposite an end of the nonconductive plug housing where the terminal end is located; a first plug terminal may be located at the plug end and include at least two electrically conductive contact pads with each contact pad of the first plug terminal extending parallel to the plug housing central axis and positioned around the plug housing central axis; and a second plug terminal may be located at the plug end and include at least two electrically conductive contact pads, each contact pad of the second plug terminal extending parallel to the plug housing central axis and positioned around the plug housing central axis, the first plug terminal located closer to the plug housing central axis than the second plug terminal and each contact pad of the first plug terminal separated from the contact pads of the second plug terminal by an electrically nonconductive medium. 
     The connector of the system may further include a connection test terminal located at the plug end closer to the connector central axis than contact pads of the first plug terminal and configured to be electrically connected to the second connector terminal when the connector is mated with the plug. 
     The connector may be configured to mate with the plug in two or more orientations and make an electrical connection to the plug in each of the two or more orientations, each of the two or more orientations corresponding to a different position of the connector relative to the plug, each different position achieved by rotating the connector around the connector central axis. 
     The outer sidewall of the electrical contact housing and the inner sidewall of the electrical contact housing may be concentric. 
     The at least one electrically conductive contact surface of the first connector terminal and the at least one electrically conductive contact surface of the second connector terminal may be concentric. 
     The connector of the system may further include a connection test terminal located closer to the connector central axis than the first connector terminal and configured to be electrically connected to the first plug terminal when the connector is mated with the plug. 
     The plug of the system may be configured to mate with the connector when the connector is in one of two or more orientations and the plug is configured to make an electrical connection to the connector in each of the two or more orientations. Each of the connector&#39;s two or more orientations corresponds to a different position of the connector relative to the plug, each different position of the connector relative to the plug achieved by rotating the connector around the plug housing central axis. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar elements. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not intended to convey any information regarding the actual shape of the particular elements, and they have been solely selected for ease of recognition in the drawings. 
         FIG. 1  is a schematic view illustrating receipt of a portable electrical energy storage device including an electrical connector in accordance with embodiments described herein by an electrically powered device including an electrical connector plug in accordance with embodiments described herein; 
         FIG. 2  is a cross-section view along line  2 - 2  in  FIG. 3  of an electrical connector base according to one non-limiting illustrated embodiment of the subject matter described herein; 
         FIG. 3  is an exploded view of the connector base illustrated in  FIG. 2 ; 
         FIG. 4  is a perspective view of an electrical connector plug in accordance with one non-limiting illustrated embodiment of the subject matter described herein; 
         FIG. 5  is a cross-section view of the electrical connector plug illustrated in  FIG. 4  taken along line  5 - 5 ; 
         FIG. 6  is an exploded view of the electrical connector plug illustrated in  FIG. 4 ; 
         FIG. 7  is a cross-section of the electrical connector base illustrated in  FIG. 2  and the electrical connector plug illustrated in  FIG. 4  in a mated configuration; 
         FIG. 8  is a schematic view illustrating receipt of a portable electrical energy storage device including an electrical connector base in accordance with embodiments described herein by an electrically powered device including an electrical connector plug in accordance with additional embodiments described herein; 
         FIG. 9A  is a cross-section view of an electrical connector base according to another non-limiting illustrated embodiment of the subject matter described herein taken along line  9 A- 9 A in  FIG. 9B ; 
         FIG. 9B  is an exploded view of the electrical connector base illustrated in  FIG. 9A ; 
         FIG. 10A  is a perspective view of an electrical connector plug in accordance with one non-limiting illustrated embodiment of the subject matter described herein; 
         FIG. 10B  is a cross-section view of the electrical connector plug illustrated in  FIG. 10A  taken along line  10 B- 10 B in  FIG. 10A ; 
         FIG. 10C  is an exploded view of the electrical connector plug illustrated in  FIG. 10A ; 
         FIG. 11  is a cross-section of the electrical connector base illustrated in  FIG. 10A  and the electrical connector plug illustrated in  FIG. 8  in a mated configuration; 
         FIGS. 12A-12C  are schematic illustrations of non-limiting illustrated embodiments of electrical connection terminals located on a portable electrical energy storage device and electrical connection terminals located on a device to be powered by the portable electrical energy storage device or a device for charging such portable electrical energy storage device; 
         FIGS. 13A-13E  are schematic illustrations of further non-limiting illustrated embodiments of electrical connection terminals located on a portable electrical energy storage device and electrical connection terminals located on a device to be powered by such portable electrical energy storage device or a device for charging such portable electrical energy storage device; 
         FIGS. 14A-14D  are schematic illustrations of additional non-limiting illustrated embodiments of electrical terminals located on a portable electrical energy storage device and electrical connection terminals located on a device to be powered by such portable electrical energy storage device or a device for charging such portable electrical energy storage device; 
         FIG. 15  is a cross-section view of an electrical connector base according to another non-limiting illustrated embodiment of the subject matter described herein taken along line  15 A- 15 A in  FIG. 16 ; 
         FIG. 16  is an exploded view of the electrical connector base illustrated in  FIG. 15 ; 
         FIG. 17  is a top view of a crown spring connector according to a non-limiting embodiment of the subject matter described herein; 
         FIG. 18  is a perspective view of the crown spring connector of  FIG. 17 ; 
         FIG. 19A  is a perspective view of an electrical connector plug in accordance with another non-limiting illustrated embodiment of the subject matter described herein; 
         FIG. 19B  is a cross-section view of the electrical connector plug illustrated in  FIG. 19A  taken along line  19 B- 19 B in  FIG. 19A ; 
         FIG. 19C  is an exploded view of the electrical connector plug illustrated in  FIG. 19A ; 
         FIG. 20  is a cross-section of the electrical connector base illustrated in  FIG. 19A  and the electrical connector plug illustrated in  FIG. 15  in a mated configuration; 
         FIG. 21  is an enlarged view of a portion of the electrical connector plug illustrated in  FIG. 19A ; 
         FIG. 22  is an enlarged view of a portion of the electrical connector plug illustrated in  FIGS. 19A and 21  with a portion removed to better illustrate features of the illustrated embodiment; and 
         FIG. 23  is an exploded view of a portion of the electrical connector plug illustrated in  FIG. 22 . 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that, although specific embodiments of the present disclosure are described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure is not limited except as by the appended claims. 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with portable electrical energy storage devices, batteries, super- or ultra-capacitors, electrical terminals, devices to be powered by portable electrical energy storage devices, devices for charging portable electrical energy storage devices and electrical connectors for electrically connecting portable electrical energy storage devices and devices to be powered by such portable electrical energy storage devices or devices for charging such portable electrical energy storage devices have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases in “one embodiment” or in “an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
     The use of ordinals such as first, second and third does not necessarily imply a ranked sense of order, but rather may only distinguish between multiple instances of an act or structure. 
     In the figures, identical reference numbers identify similar features or elements. The sizes and relative positions of the features in the figures are not necessarily drawn to scale. 
     Reference to portable electrical power storage device or portable electrical energy storage device means any device capable of storing electrical power and releasing stored electrical power including but not limited to batteries and super or ultra-capacitors. Reference to batteries means a chemical storage cell or cells, for instance rechargeable or secondary battery cells including but not limited to nickel cadmium alloy or lithium ion battery cells. Chemistries besides nickel cadmium alloy or lithium ion are also included in the reference to batteries or chemical storage cells. 
     Reference throughout the specification to an electric powered device includes devices that can be powered by a portable electrical energy storage device and devices that are electrically powered from a source other than a portable electrical energy storage device, e.g., a device for electrically charging a portable electrical energy storage device. 
     Referring to  FIG. 1 , a portable electrical energy storage device in the form of a battery pack  10  includes a battery pack housing  12 . Though not illustrated, contained within battery pack housing  12  are one or more individual portable electrical energy storage devices. These individual portable electrical energy storage devices can be arranged in different configurations, including single or multiple layers, with each layer including one or more individual electrical energy storage devices. In the illustrated exemplary embodiment of  FIG. 1 , battery pack  10  has a cylindrical shape. A cross-section of the battery pack  10  along line  2 - 2  has a round cross-section in the illustrated embodiment. As will become apparent based on descriptions that follow, battery packs of the type described herein are not limited to battery packs that are cylindrical and have a round cross-section; battery packs having different shapes and cross-sections are included in the embodiments described herein. Battery packs having polygonal, e.g., square or rectangular, cross-sections are examples of different shaped battery packs that are included within the description of battery packs of the type described herein. 
     At one end, battery pack  10  includes a handle  14  attached to the top of battery pack  10  for grasping battery pack  10 . At an end of battery pack  10  opposite the end containing handle  14 , battery pack  10  includes a multidirectional electrical connector  16  shown in phantom lines. Multidirectional electrical connector  16  is represented schematically and is not limited to the shape illustrated in phantom lines, and can have a shape different than that shown in phantom lines in  FIG. 1 . 
     In the embodiment illustrated in  FIG. 1 , battery pack  10  is configured to cooperate with a battery pack receptacle  18  which includes an electrical connector plug  20 . Electrical connector plug  20  is represented schematically in  FIG. 1  and is not limited to the shape illustrated in phantom lines and can have a shape different than that shown in  FIG. 1 . Receptacle  18  is sized and configured to receive battery pack  10  when the battery pack  10  is moved in the direction of arrow  23  in  FIG. 1 . An advantage of the electrical connector  16  and the electrical connector plug  20  is their ability to electrically connect to each other regardless of the rotational position of battery pack  10  relative to battery receptacle  18  when the battery receptacle  18  receives battery pack  10 . The ability to achieve an electrical connection between electrical connector  16  and electrical connector plug  20  regardless of the rotational orientation of the battery pack  10  relative to battery pack receptacle  18  reduces the likelihood that an ineffective electrical connection between electrical connector  16  and electrical connector plug  20  results due to insertion of a battery pack  10  into battery pack receptacle  18  in an improper orientation. Thus, in accordance with embodiments described herein, electrical connector  16  and electrical connector plug  20  provide a multidirectional electrical connection system which can make an electrical connection in a plurality of rotational orientations without compromising the quality and safety of the electrical connection due to insertion of a battery pack  10  into battery pack receptacle  18  in an improper orientation. 
     Specific embodiments are described herein with reference to connectors for electrically connecting portable electrical energy storage device(s) to an electrical system of electrically powered vehicles and devices for charging portable electrical energy storage devices; however, the present disclosure and the reference to connectors for electrically connecting a portable electrical energy storage device to an electrical system of electrically powered vehicles and devices for charging the portable electrical energy storage devices is not limited to electrical systems for electrically powered vehicles or devices for charging portable electrical energy storage devices. Connectors of the type described herein are also useful for electrically connecting portable electrical energy storage devices to electrical systems of electrically powered devices other than electrically powered vehicles and devices for charging the portable electrical energy storage devices. Connectors of the type described herein for use in providing an electrical connection between a portable electrical energy storage device and an electrical system of an electrically powered vehicle are capable of safely carrying electrical currents levels sufficient to drive a traction electric motor of the vehicle. For example, electric connectors of the type described herein safely carry electric current ranging from about 30 amps or more. In certain embodiments the electrical connectors can safely carry about 50 amps or more, about 75 amps or more, about 100 amps or more, about 200 amps or more, about 300 amps or more, about 400 amps or more, about 500 amps or more. In some embodiments the electrical connector can safely carry about 1000 amps or more. 
     Details of one embodiment of the present disclosure are described below with reference to  FIGS. 2 and 3 .  FIGS. 2 and 3  illustrate one exemplary embodiment of an electrical connector  16  electrically connected to a portable electrical energy storage device or to a device to be powered by the portable electrical energy storage device. Connector  16  in the illustrated exemplary embodiment includes an electrically nonconductive connector base  19 , a first terminal  21 , a second terminal  22 , and an electrical connection test terminal  24 . In order to avoid obscuring aspects of the subject matter described herein, details of how first terminal  21  and second terminal  22  are electrically connected to the portable electrical energy storage device or an electrically powered device are omitted. 
     Electrically nonconductive connector base  19  includes a conductor base outer wall  26 . In the illustrated exemplary embodiment of  FIGS. 2 and 3 , electrically nonconductive connector base  19  is circular in shape when viewed along a longitudinal axis  32 . The electrically nonconductive connector base  19  including conductor base outer wall  26  is formed from a nonconductive material, such as plastic. Conventional techniques such as extrusion or injection molding can be used to form nonconductive connector base  19  and conductor base outer wall  26 . Connector base  19  further includes an electrical terminal outer wall  28  and an electrical terminal inner wall  30 . Electrical terminal outer wall  28  and electrical terminal inner wall  30  are also formed of an electrically nonconductive material. In the illustrated embodiment of  FIGS. 2 and 3 , electrical terminal outer wall  28  and electrical terminal inner wall  30  are integral with conductor base outer wall  26 . Thus, in the illustrated embodiment, electrically nonconductive connector base  19  is an integral element; however, electrically nonconductive connector base  19  need not be an integral element, for example, conductor base outer wall  26 , electrical terminal outer wall  28  and electrical terminal inner wall  30  can be formed individually and attached to each other in different combinations. In the illustrated exemplary embodiments of  FIGS. 2 and 3 , electrical terminal outer wall  28  and electrical terminal inner wall  30  are circular in shape when viewed along a longitudinal axis  32  and are positioned concentrically relative to conductor base outer wall  26 . In  FIGS. 2 and 3 , electrical terminal inner wall  30  is spaced radially inward from electrical terminal outer wall  28  and is separated therefrom by an air gap  34 . Electrical terminal outer wall  28  is spaced radially inward from conductor base outer wall  26  and is separated therefrom by an air gap  36 . Air gap  34  provides an electrically nonconductive medium between electrical terminal inner wall  30  and electrical terminal outer wall  28 . Air gap  36  provides an electrically nonconductive medium between electrical terminal outer wall  28  and conductor base outer wall  26 . 
     Electrical terminal inner wall  30  includes an inner surface  38  and an outer surface  40 . Inner surface  38  of electrical terminal inner wall  30  is located closer to longitudinal axis  32  than outer surface  40  of electrical terminal inner wall  30 . Electrical terminal outer wall  28  includes an inner surface  42  and an outer surface  44 . Inner surface  42  of electrical terminal outer wall  28  is located closer to longitudinal axis  32  than outer surface  44  of electrical terminal outer wall  28 . 
     Inner surface  38  of electrical terminal inner wall  30  includes first electrically conductive terminal  21 . In the illustrated exemplary embodiment, first electrically conductive terminal  21  is a ring-shaped member conforming in size and shape to the inner surface  38  of electrical terminal inner wall  30 . The bottom edge of electrically conductive terminal  21  is electrically connected to a first terminal connector  46  which lies beneath the electrical terminal inner wall  30 , electrical terminal outer wall  28  and conductor base outer wall  26 . First terminal connector  46  can be electrically connected to a portable electrical energy storage device, a device to be powered by a portable electrical energy storage device or a device for charging a portable electrical energy storage device, thus providing an electrical connection between the device connected to the first terminal connector  46  and the other devices. 
     Inner surface  42  of electrical terminal outer wall  28  includes second electrically conductive terminal  22 . In the illustrated exemplary embodiment, second electrically conductive terminal  22  is a ring-shaped member conforming to the size and shape of inner surface  42  of electrical terminal outer wall  28 . The bottom edge of electrically conductive terminal  22  is electrically connected to a second electrical terminal connector  48  which lies beneath the electrical terminal outer wall  28  and conductor base outer wall  26 . Second terminal connector  48  can be electrically connected to a portable electrical energy storage device, a device to be powered by the portable electrical energy storage device, or a device for charging a portable electrical energy storage device, thus providing an electrical connection between the device connected to the second terminal connector  48  and the other devices. 
     In the exemplary embodiment illustrated in  FIGS. 2 and 3 , first electrically conductive terminal  21  and second electrically conductive terminal  22  are illustrated as a single terminal, respectively; however, embodiments of the present disclosure are not limited to first electrically conductive terminal  21  and electrically conductive terminal  22  including an integral continuous contact pad. First electrically conductive terminal  21  and second electrically conductive terminal  22  can take different forms, such as a terminal that includes more than one contact pad. An example of such type of terminal having more than one contact pad is illustrated in  FIGS. 9A and 9B . In addition, while first electrically conductive terminal  21  is illustrated in  FIGS. 2 and 3  as being connected to a single first terminal connector  46 , first electrically conductive terminal  21  can be electrically connected to more than one first terminal connector  46 . Similarly, while second electrically conductive terminal  22  is illustrated in  FIGS. 2 and 3  as being connected to a single second terminal connector  48 , second electrically conductive terminal  22  can be electrically connected to more than one second terminal connector  48 . When first electrically conductive terminal  21  and/or second electrically conductive terminal  22  are provided in the form of a terminal that includes more than one contact pad, each individual contact pad can be connected to its own first terminal connector  46  or its own second terminal connector  48 . 
     In the illustrated embodiment of  FIGS. 2 and 3 , electrical connection test terminal  24  of electrical connector  16  is an electrically conductive member in the shape of a cylinder centered along longitudinal axis  32 . Electrical connection test terminal  24  is positioned radially inward of first electrically conductive terminal  21 . The top of electrical connection test terminal  24  is recessed below the upper surfaces of a conductor base outer wall  26 , electrical terminal outer wall  28 , electrical terminal inner wall  30 , first electrically conductive terminal  21  and second electrically conductive terminal  22 . The center of electrical connection test terminal  24  includes a bore that passes through electrical connection test terminal  24  along a longitudinal axis  32 . Electrical connection test terminal  24  is electrically connected to connection test terminal connector  50  which is located below conductor base outer wall  26 , electrical terminal outer wall  28 , and electrical terminal inner wall  30 . In the illustrated embodiment, electrical test connection terminal  24  is electrically connected to connection test terminal connector  50  at its bottom; however, electrical connection between electrical test connection terminal  24  and connection test terminal connector  50  need not be at the bottom of connection test terminal connector  50 . Connection between connection test terminal connector  50  and electrical test connection terminal  24  can occur at different locations along the body of electrical test connection terminal  24 . Connection test terminal connector  50  provides electrical connection between electrical test connection terminal  24  and the electrical sensing device that can be connected to connection test terminal connector  50 . 
     Referring to  FIGS. 4, 5 and 6 , an exemplary electrical connector plug  20  in accordance with embodiments described herein is illustrated. Electrical connector plug  20  includes a nonconductive plug housing or body  100 , a first electrical connection terminal  102  and a second electrical connection terminal  104 . The electrical connection plug housing  100 , first electrical connection terminal  102  and second electrical connection terminal  104  are sized and configured to mate with electrical connector  16  described above with reference to  FIGS. 2 and 3 . When mated, an electrical connection is provided between a device electrically connected to electrical connector  16  and a device connected to electrical connector plug  20 . 
     Nonconductive plug housing body  100  is an electrically nonconductive material, such as an electrically nonconducting plastic, and has a cylindrical shape centered along plug housing longitudinal axis  111 . At a plug end  107 , a first electrical connection terminal  102  and a second electrical connection terminal  104  protrude from nonconductive plug housing body  100 . First electrical connection terminal  102  and second electrical connection terminal  104  are formed out of an electrically conductive material, such as an electrically conductive metal. At the opposite terminal end  105  of nonconductive plug housing  100 , a first terminal connector  106  and a second terminal connector  108  protrude from nonconductive plug housing  100 . First terminal connector  106  and second terminal connector  108  are formed out of an electrically conductive material, such as an electrically conductive metal. Intermediate first connection terminal  102  and first terminal connector  106  comprise a first terminal body  110 . First terminal body  110  is formed out of an electrically conductive material, such as an electrically conductive metal. First terminal body  110  provides an electrical connection between a first connection terminal  102  and first terminal connector  106 . Intermediate second connection terminal  104  and second terminal connector  108  comprise a second terminal body  112 . Second terminal body  112  is formed out of an electrically conductive material, such as an electrically conductive metal. Second terminal body  112  provides an electrical connection between the second connection terminal  104  and second terminal connector  108 . In order to avoid obscuring aspects of the subject matter described herein, details of how first terminal connector  106  and second terminal connector  108  are electrically connected to a portable electrical energy storage device or an electrically powered device are omitted. 
     The specific example of embodiments described herein illustrated in  FIGS. 4-6  illustrates a first terminal body  110  that is offset radially from the plug housing longitudinal axis  111 . Similarly, secondary terminal body  112  is offset radially from the plug housing longitudinal axis  111 . In addition to the specific examples of the shapes and locations of first terminal body  110  and second terminal body  112  illustrated in  FIGS. 4-6 , first terminal body  110  and second terminal body  112  can be shaped differently and located in other locations. For example, first terminal body  110  could be annular shaped like second terminal body  112  or a different shape, and/or second terminal body  112  need not be annular shaped, for example, second terminal body  112  could have a shape similar to first terminal body  110  or a different shape. 
     First electrical connection terminal  102  is annular in shape. Second electrical connection terminal  104  is also annular in shape and has a diameter greater than the diameter of the first electrical connection terminal  102 . In the illustrated embodiment, first electrical connection terminal  102  and second electrical connection terminal  104  are concentric relative to each other. First electrical connection terminal includes an inner electrical contact pad surface  114  and an outer electrical contact pad surface  116 . Similarly, second electrical connection terminal  104  includes an inner electrical contact pad surface  118  and an outer electrical contact pad surface  120 . In the illustrated embodiment, inner electrical contact pad surface  114  and outer electrical contact pad surface  116  are separated by an electrically nonconductive medium, e.g., air or an electrically nonconductive plastic. 
     In the exemplary embodiment illustrated in  FIGS. 4-6 , first electrical connection terminal  102  and second electrical connection terminal  104  are illustrated as a single terminal, respectively; however, embodiments of the present disclosure are not limited to first electrical connection terminal  102  and second electrical connection terminal  104  being in the form of a single integral terminal. First electrical connection terminal  102  and second electrical connection terminal  104  can take different forms, such as a terminal that includes more than one contact pad. An example of such type of terminal is illustrated in  FIGS. 10A-10C . In addition, while first electrical connection terminal  102  is illustrated in  FIGS. 4-6  as being connected to a single first terminal connector  106 , a plurality of first terminal connectors  106  can be provided and electrical connection terminal  102  connected to more than one first terminal connector  106 . In addition, first terminal connector  106  can be of a different shape than illustrated in  FIGS. 4-6  and first terminal body  110  can be of a different shape than illustrated in  FIGS. 4-6 . Similarly, while second electrical connection terminal  104  is illustrated in  FIGS. 4-6  as being connected to a single second terminal connector  108 , second electrical connection terminal  104  can be electrically connected to more than one second terminal connector  108 . Furthermore when first electrically first electrical connection terminal  102  and/or second electrical connection terminal  104  are provided in the form of a terminal that includes more than one electrical contact pad, the individual contact pads can be electrically isolated from other contact pads and electrically connected to different first terminal connectors  106  and second terminal connectors  108 , respectively. 
     Referring to  FIG. 7 , electrical connector  16  of  FIGS. 2-3  and electrical connector plug  20  of  FIGS. 4-6  are illustrated in a mated configuration. In  FIG. 7 , outer electrical contact pad surface  116  of first electrical connection terminal  102  makes an electrical connection with first electrically conductive terminal  21  by contacting the exposed surface of first electrically conductive terminal  21 . Outer electrical contact pad surface  120  of second electrical connection terminal  104  makes an electrical connection with second electrically conductive terminal  22  of electrical connector  16  by contacting the exposed surface of second electrically conductive terminal  22 . As a result, a portable electrical energy storage device or a device to be powered by or charge such portable electrical energy storage device that is connected to electrical connector  16  is electrically connected to a portable electrical energy storage device or a device to be powered by or charge such portable electrical energy storage device that is connected to electrical connector plug  20 . Referring to the embodiments illustrated in  FIG. 1 , the shape of the electrical connector  16  and electrical connector plug  20  permit the insertion of a portable electrical energy storage device into a receptacle for the portable electrical energy storage device in an unlimited number of rotational orientations, while still establishing an effective and safe electrical connection between the electrical connector  16  and the electrical connector plug  20 . 
     As seen in  FIG. 7 , when electrical connector  16  is mated with electrical connector plug  20 , electrical connection test terminal  24  comes into electrical contact with inner electrical contact pad surface  114  of connection plug  20 . When electrical connection test terminal  24  electrically contacts inner electrical contact pad surface  114  when outer electrical contact pad surface  116  is in electrical contact with first electrically conductive terminal  21  of electrical connector  16 , electrical connection test terminal  24  is at the same voltage as first electrically conductive terminal  21 . This voltage can be detected by a sensor connected to connection test terminal connector  50 . Detection of this voltage provides a confirmation that first electrical connection terminal  102  of connection plug  20  is electrically connected to first electrically conductive terminal  21  of electrical connector  16 . 
     As seen in  FIG. 7 , when electrical connector  16  is mated with electrical connector plug  20 , electrical connection test terminal  24  of electrical connector  16  makes electrical contact with inner electrical contact pad surface  114  of connection plug  20 . When electrical connection test terminal  24  electrically contacts inner electrical contact pad surface  114  when outer electrical contact pad surface  116  is in electrical contact with first electrically conductive terminal  21  of electrical connector  16 , electrical connection test terminal  24  is at the same voltage as first electrically conductive terminal  21 . The electrical connection test terminal  24  is connected to one terminal of a voltage sensor (not shown) via connection test terminal connector  50  for connection test terminal  24 . Second electrically conductive terminal  22  is electrically connected to the other terminal of the voltage sensor (not shown) via second terminal connector  48 . The voltage sensor is configured to detect the voltage between electrical connection test terminal  24  and second electrically conductive terminal  22 . When electrical connector  16  is electrically connected to a portable electrical energy storage device, comparison of this detected voltage to the voltage of the portable electrical energy storage device to which electrical connector  16  is connected provides an indication of whether an electrical contact has been established between first electrically conductive terminal  21  of electrical connector  16  and first electrical connection terminal  102  of electrical connector plug  20 . An electrical connection between these terminals will be indicated by the voltage detected by the voltage sensor being substantially equal to the voltage of the portable electrical energy storage device. When electrical connector  16  is electrically connected to a device to be powered by or charge a portable electrical energy storage device and the electrical connector plug  20  is electrically connected to the portable electrical energy storage device, comparison of the voltage detected by the voltage sensor to the voltage of the portable electrical energy storage device provides an indication of whether an electrical contact has been established between first electrically conductive terminal  21  of electrical connector  16  and first electrical connection terminal  102  of electrical connector plug  20  and between second electrically conductive terminal  22  of electrical connector  16 , second electrical connection terminal  104  of electrical connector plug  20  and second electrical conductive terminal  22  of electrical connector  16 . 
     The present description has not identified the polarity of the first electrically conductive terminal  21  and second electrically conductive terminal  22  of the electrical connector  16  or the polarity of the first electrical connection terminal  102  and the second electrical connection terminal  104  of the electrical connector plug  20 . In accordance with embodiments described herein, the polarity of the different terminals can vary provided the first electrically conductive terminal  21  of electrical connector  16  is of the same polarity as the first electrical connection terminal  102  of the electrical connector plug  20 . Similarly, the polarity of the second electrical conductive terminal  22  of electrical connector  16  should be of the same polarity as the second electrical connection terminal  104  of the electrical connector plug  20 . 
     Referring to  FIG. 8 , another example of an electrical connector  126  and the electrical connector plug  128  in accordance with embodiments described herein is illustrated. In  FIG. 8 , a battery pack  122  includes an electrical connector  126 , and a battery pack receptacle  124  includes an electrical connector plug  128 . Like battery pack  10  of  FIG. 1 , the battery pack  122  contains one or more individual portable electrical energy storage devices. These portable electrical energy storage devices can be arranged in different configurations, including single or multiple layers of individual electrical energy storage devices, each layer including one or more individual portable electrical energy storage devices. Battery pack  122  has a cross-section taken along line  9 A- 9 A that has a shape that is not round, e.g., polygonal. In the illustrated embodiment the battery pack  122  has a cross-section taken along line  9 A- 9 A that is square. Battery packs in accordance with embodiments described are not limited to those that have a square cross-section as shown in  FIG. 8 , but include battery packs that have a cross-section of a different polygonal shape, e.g., rectangular, triangular, pentagonal, hexagonal, heptagonal, octagonal and the like. Battery packs in accordance with embodiments described herein can have a cross-section that includes more than eight sides. Like battery pack  10  described with reference to  FIGS. 1-7  which can be received in battery pack receptacle  18  in more than one rotational orientation, battery pack  122  can be received in battery pack receptacle  124  in more than one rotational orientation. For example, illustrated battery pack  122  can be received in battery pack receptacle  124  in up to four different rotational orientations by rotating the battery pack in the direction of arrow  130 . 
     At one end, battery pack  122  includes a handle  132  attached to the battery pack  122 . At an end of battery pack  122  opposite the end containing handle  132 , battery pack  122  includes a multidirectional electrical connector  126  shown in phantom lines. Multidirectional electrical connector  126  is represented schematically and can have a different shape than that shown in phantom lines in  FIG. 8 . Receptacle  124  is sized and configured to receive battery pack  122  when a battery pack  122  is moved in the direction of arrow  134  in  FIG. 8 , and includes electrical connector plug  128 . Electrical connector plug  128  is represented schematically in  FIG. 8  and can have a different shape than that shown in  FIG. 8 . An advantage of electrical connector  126  and electrical connector plug  128  is their ability to cooperate with each other and electrically connect to each other when battery pack  122  is received in battery pack receptacle  124  in multiple rotational orientations. The ability to achieve an electrical connection between electrical connector  126  and electrical connector plug  128  in multiple rotational orientations of battery pack  122  relative to battery pack receptacle  124  reduces the likelihood that an ineffective electrical connection between electrical connector  126  and electrical connector plug  128  will result due to insertion of the battery pack  122  into battery pack receptacle  124  in an improper orientation. Thus, in accordance with embodiments described herein, electrical connector  126  and electrical connector plug  128  provide a multidirectional electrical connection system capable of providing an effective electrical connection in a plurality of rotational orientations whose effectiveness is not compromised due to insertion of a battery pack  122  into battery pack receptacle  124  in an improper orientation. 
     As with battery connector  16  illustrated in  FIG. 1 , specific embodiments are described herein with reference to connectors for electrically connecting portable electrical energy storage devices to an electrical system of electrically powered vehicles or devices for charging the portable electrical energy storage devices; however, the present disclosure and the reference to connectors for electrically connecting a portable electrical energy storage device to an electrical system of electrically powered vehicles or devices for charging the portable electrical energy storage devices is not limited to electrical systems for electrically powered vehicles or devices for charging portable electrical energy storage devices. Connectors of the type described herein are also useful for electrically connecting a portable electrical energy storage device to electrical systems of electrically powered devices other than electrically powered vehicles and devices for charging the portable electrical energy storage devices. 
     Details of another embodiment of the present disclosure are described below with reference to  FIGS. 9A-9B, 10A-10C and 11 .  FIGS. 9A-9B, 10A-10C and 11  illustrate one exemplary embodiment of an electrical connector  126  electrically connected to a portable electrical energy storage device or to a device to be powered by or for charging the portable electrical energy storage device and an electrical connector plug  128  connected to a portable electrical energy storage device or to a device to be powered by or for charging the portable electrical energy storage device that is not connected to the electrical connector  126 . Electrical connector  126  in the illustrated exemplary embodiment includes an electrically nonconductive connector base  136 , a first electrically conductive terminal  138 , a second electrically conductive terminal  140 , and an electrical connection test terminal  142 . 
     Electrically nonconductive connector base  136  includes a connector base outer wall  144 . In the illustrated exemplary embodiment of  FIGS. 9A-9B, 10A-10C and 11 , electrically nonconductive connector base  136  is circular in shape when viewed along its longitudinal axis  147 . The electrically nonconductive connector base  136  including connector base outer wall  144  is formed of a nonconductive material, such as plastic. Conventional techniques such as extrusion or injection molding can be used to form nonconductive connector base  136  and connector base outer wall  144 . Electrically nonconductive connector base  136  further includes an annular shaped electrical contact housing  146  that includes an inner surface  148  and an outer surface  150 . Electrical contact housing  146  is formed out of an electrically nonconductive material, such as an electrically nonconductive plastic. In the illustrated embodiment, the electrical contact housing  146  is integral with the electrically nonconductive connector base  136 . Thus, in the illustrated embodiment, electrically nonconductive connector base  136  including connector base outer wall  144  and electrical contact housing  146  is an integral element; however, electrically nonconductive connector base  136  need not be an integral element, for example, conductive base outer wall  144  and electrical contact housing  146  can be formed separately and attached to each other. In the exemplary embodiment illustrated in  FIG. 9A , annular shaped electrical contact housing  146  is a quadrilateral with equal opposing angles when viewed along longitudinal axis  147 . In the illustrated embodiment, the quadrilateral has all sides of equal length. Annular shaped electrical contact housing  146  can be of other polygonal shapes besides a square, for example, annular shaped electrical contact housing  146  can have the shape of a rectangle, pentagon, hexagon, heptagon, octagon or other polygon with more than eight sides. Inner surface  148  of the electrical contact housing  146  is located closer to longitudinal axis  147  than outer surface  150  of the electrical contact housing  146 . Outer surface  150  of the electrical contact housing  146  is separated from connector base outer wall  144  by an electrically nonconductive medium, such as air or other electrically nonconductive medium, such as a nonconductive plastic. 
     Inner surface  148  of electrical contact housing  146  includes first electrically conductive terminal  138 . In the illustrated exemplary embodiment, first electrically conductive terminal  138  is a ring-shaped member conforming to the shape of the inner surface  148  of the electrical contact housing  146 . First electrically conductive terminal  138  includes a plurality of electrical contact pads  152 . In the exemplary embodiment illustrated in  FIGS. 9A and 9B , first electrically conductive terminal  138  includes four electrical contact pads  152 , one positioned on each of the four inner surfaces  148  of the square shaped annular electrical contact housing  146 . First electrically conductive terminal  138  can include more than four or less than four electrical contact pads  152 . Embodiments described herein are not limited to first electrically conductive terminal  138  including four electrical contact pads  152 . As illustrated in  FIG. 9B , the contact pads  152  of first electrically conductive terminal  138  are electrically connected along their base. In the illustrated embodiment, first electrically conductive terminal  138  is electrically connected at its base to a first terminal connector  154 . First terminal connector  154  can be electrically connected to a portable electrical energy storage device or a device to be powered by or for charging the portable electrical energy storage device, thus providing an electrical connection between the portable electrical energy storage device or the device to be powered by or for charging the portable electrical energy storage device and the first electrically conductive terminal  138 . 
     Outer surface  150  of electrical contact housing  146  includes a second electrical conductive terminal  140 . In the illustrated exemplary embodiment, second electrical conductive terminal  140  is a ring-shaped member conforming to the shape of outer surface  150  of the electrical contact housing  146 . Second electrically conductive terminal  140  includes a plurality of electrical contact pads  156 . In the exemplary embodiment illustrated in  FIGS. 9A and 9B , second electrically conductive terminal  140  includes four electrical contact pads  156 , one positioned on each of the four outer surfaces  150  of the square shaped annular electrical contact housing  146 . Second electrically conductive terminal  140  can include more than four or less than four electrical contact pads  156 . Embodiments described herein are not limited to second electrical conductive terminal  140  including four electrical contact pads  156 . As illustrated in  FIG. 9B , contact pads  156  of second electrically conductive terminal  140  are electrically connected along their base. Second electrically conductive terminal  140  is electrically connected at its base to a second terminal connector  158 . Second terminal connector  158  can be electrically connected to a portable electrical energy storage device or a device to be powered by or for charging a portable electrical energy storage device, thus providing an electrical connection between the portable electrical energy storage device or the device to be powered by or for charging the portable electrical energy storage device and the second electrically conductive terminal  140 . In order to avoid obscuring aspects of the subject matter described herein, details of how first terminal connector  154  and second terminal connector  158  are electrically connected to a portable electrical energy storage device or an electrically powered device are omitted. 
     In the exemplary embodiment illustrated in  FIGS. 9A and 9B , electrical connection test terminal  142  of electrical connector  126  is an electrically conductive member in the shape of a cylinder centered along longitudinal axis  147 . Electrical connection test terminal  142  is positioned radially inward of first electrically conductive terminal  138 . The upper surface of electrical connection test terminal  142  is recessed below the upper surfaces of conductive base outer wall  144 , electrical contact housing  146 , first electrically conductive terminal  138  and second electrically conductive terminal  140 . Electrical connection test terminal  142  is electrically connected to connection test terminal connector  160 . In the illustrated embodiment, electrical connection test terminal  142  is electrically connected to connection test terminal connector  160  at its bottom; however, electrical connection between electrical connection test terminal  142  and connection test terminal connector  160  need not be at the bottom of connection test terminal  142 . Connection between connection test terminal  142  and electrical connection test terminal connector  160  can occur at different locations along the body of electrical connection test terminal  142 . 
     Referring to  FIGS. 10A-10C and 11 , an exemplary electrical connector plug  128  in accordance with embodiments described herein is illustrated. Electrical connector plug  128  includes a nonconductive plug housing  162 , a first electrical terminal  164  and a second electrical terminal  166 . The first electrical terminal  164  and second electrical terminal  166  are sized and shaped to mate with the electrical connector  126  and its respective components. When mated, electrical connection is made between electrical connector  126  and electrical connector plug  128 . 
     Nonconductive plug housing  162  includes a plug body  170  comprising an electrically nonconductive material, such as an electrically nonconductive plastic. Plug body  170  has a cylindrical shape and is centered along plug housing longitudinal axis  168 . From one end of plug body  170  (the top end in  FIG. 10A ), first electrical terminal  164  and a second electrical terminal  166  protrude. First electrical terminal  164  and second electrical terminal  166  are formed out of an electrically conductive material, such as an electrically conductive metal. At the end of plug body  170  where first electrical terminal  164  and second electrical terminal  166  protrude, an annular terminal housing  172  protrudes from plug body  170  beyond the ends of first electrical terminal  164  and second electrical terminal  166 . In the embodiment illustrated in  FIG. 10A , annular terminal housing  172 , when viewed along longitudinal axis  168 , has a round shape; however, the shape of annular terminal housing is not limited to a round shape. For example, when the shape of the gap between outer surface  150  of electrical contact housing  146  and conductor-base inner wall  145  of connector  126  in  FIG. 9A  is something other than round, annular terminal housing  172  will have a complementary non-round shape. For example, if the shape of the gap between the outer surface  150  of the electrical contact housing  146  and conductor base inner wall  145  is square, annular terminal housing  172  will have a complementary square shape and will be sized to be received into that gap. One of the reasons the shapes are complementary is so annular terminal housing  172  can be received into the gap between outer surface  150  of electrical contact housing  146  and conductor base inner wall  145 , thus allowing connector  126  and plug  128  to mate with each other. 
     At the end of nonconductive plug housing  162  opposite annular terminal housing  172  (the bottom end in  FIG. 10A ), first terminal connector  174  of first electrical terminal  164  and second terminal connector  175  of second electrical terminal  166  protrude from nonconductive plug body  170 . Alternatively, first terminal connector  174  and second terminal connector  175  do not protrude from nonconductive plug body  170 , but rather are accessible within nonconductive body  170 . In  FIG. 10B  the interior of nonconductive plug body  170  is shown as being hollow. In accordance with other embodiments described herein, nonconductive plug body  170  is filled with a nonconductive material, such as a nonconductive plastic, and the first terminal connector  174  and second terminal connector  175  extend through and protrude from this nonconductive material at an end of the nonconductive plug body  170  that is opposite annular electrical terminal housing  172 . First terminal connector  174  and second terminal connector  175  provide electrical connectors for making an electrical connection with first electrical terminal  164  and second electrical terminal  166 . In order to avoid obscuring aspects of the subject matter described herein, details of how first terminal connector  174  and second terminal connector  175  are electrically connected to the portable electrical energy storage device or an electrically powered device are omitted. 
     In the embodiment illustrated in  FIGS. 10A-10C , first electrical terminal  164  is formed out of an electrically conductive material, such as a conductive metal. When viewed along longitudinal axis  168 , first electrical terminal  164  has a square shape and includes a cylindrical bore centered on longitudinal axis  168  that passes through first electrical terminal  164 . First electrical terminal  164  may have a shape other than the illustrated square shape, for example, first electrical terminal  164  can have a circular shape when viewed along longitudinal axis  168  or it can have a polygon shape other than a square, for example, a triangle, rectangle, pentagon, hexagon, octagon, or a polygon having more than eight sides. Preferably, first electrical terminal  164  has a shape that complements the shape of the electrical contact housing  146  of electrical connector  126  in  FIG. 9A . When the shape of first electrical terminal  164  complements the shapes of the electrical contact housing  146  (e.g., the shape of first electrical terminal  164  and the shape of electrical contact housing  146  are related in a male plug/female receptacle relationship), first electrical connection terminal  164  can be received in electrical contact housing  146  and the two are able to mate with each other. 
     In the exemplary embodiment illustrated in  FIGS. 10A-10C , an inner surface of annular electrical terminal housing  172  includes a second electrical connection terminal  166 . Second electrical terminal  166  is formed out of an electrically conductive material, such as an electrically conductive metal. As illustrated in  FIG. 10C , second electrical terminal  166  includes three contact pads  178  that are offset from each other by 90° along inner surface  176  of electrical terminal housing  172 . While the exemplary embodiment of  FIGS. 10A-10C  illustrates three contact pads  178 , a greater number or a lesser number of contact pads  178  can be employed in accordance with embodiments described herein. For example, only one or two contact pads  178  can be utilized. As illustrated in  FIG. 10C , contact pads  178  are electrically connected to each other at their base  179 . In the embodiment illustrated in  FIG. 10A-10C , base  179  extends through the nonconductive plug body  170  to the end of nonconductive plug body  170  opposite annular electrical terminal housing  172 . 
     Located adjacent inner surface  176  of annular electrical terminal housing  172  is a connection test terminal  180 . Connection test terminal  180  is an electrically conductive material such as an electrically conductive metal. In the embodiment illustrated in  FIGS. 10A-10C , connection test terminal  180  is spaced apart 90° from two contact pads  178  of second electrical terminal  166  and extends from annular electrical terminal housing  172  through nonconductive plug body  170 , and in the illustrated embodiment protrudes from an end of nonconductive plug body  170  that is opposite the end of nonconductive plug body  170  adjacent annular electrical terminal housing  172 . This protruding end of connection test terminal  180  provides an electrical connector  182  for making an electrical connection to connection test terminal  180 . 
     First terminal connector  174  and second terminal connector  175  provide electrical connection points for connecting first electrical terminal  164  and second electrical terminal  166  to a portable electrical energy storage device or to a device to be powered by or for charging the portable electrical energy storage device. 
     Referring to  FIG. 11 , electrical connector  126  of  FIGS. 9A and 9B  and electrical connector plug  128  of  FIGS. 10A-10C  are illustrated in a mated configuration. In this mated configuration, first electrical terminal  138  of electrical connector  126  makes electrical contact with first electrical terminal  164  of the electrical connector plug  128 . Second electrical terminal  140  of electrical connector  126  makes electrical contact with second electrical terminal  166  of electrical connector plug  128 . As a result, a portable electrical energy storage device or a device to be powered by or for charging such portable electrical energy storage device that is connected to electrical connector  126  is electrically connected to a portable electrical energy storage device or a device to be powered by or for charging such portable electrical energy storage device that is connected to electrical connector plug  128 . 
     Referring to  FIG. 8 , the size and shape of electrical connector  126  and the complementary size and shape of electrical connector plug  128  permit a user to insert the battery pack  122  into the battery pack receptacle  124  in a plurality of rotational orientations relative to each other, while establishing a useful and safe electrical connection between the electrical connector  126  and the electrical connector plug  128 . 
     As seen in  FIG. 11 , when electrical connector  126  is mated with electrical connector plug  128 , electrical connection test terminal  142  of electrical connector  126  makes electrical contact with first electrical terminal  164  of electrical connector plug  128 . When electrical connector  126  is mated with electrical connector plug  128 , electrical connection test terminal  180  of electrical connector plug  128  makes electrical contact with second electrical terminal  140  of electrical connector  126 . Electrical connection test terminal  180  is electrically connected to one terminal of a voltage sensor (not shown) via electrical connector  182  for connection test terminal  180 . When electrical connector  126  is mated with electrical connector plug  128 , electrical connection test terminal  142  of electrical connector  126  makes electrical contact with first electrical terminal  164  of electrical connector plug  128 . Electrical connection test terminal  142  of electrical connector plug  128  is electrically connected to another terminal of the voltage sensor (not shown) via electrical connection test terminal connector  160  for connection test terminal  142 . When electrical connection test terminal  180  contacts second electrical terminal  140  and electrical connection test terminal  142  contacts first electrical terminal  164 , electrical connection test terminal  180  will be at the same voltage as second electrical terminal  140  and electrical connection test terminal  142  will be at the same voltage as first electrical terminal  164 . The voltage sensor is configured to detect the voltage between electrical connection test terminal  180  and electrical connection test terminal  142 . Comparison of this detected voltage to the voltage of the portable electrical energy storage device to which electrical connector  126  or electrical connector plug  128  are connected provides an indication of whether an electrical contact has been established between first electrical terminal  164  of electrical connector plug  128  and first electrical terminal  138  of electrical connector  126  and second electrical terminal  166  of electrical connector plug  128  and second electrical terminal  140  of electrical connector  126 . Electrical connection between these terminals will be indicated by the voltage detected by the voltage sensor being substantially equal to the voltage of the portable electrical energy storage device. The configuration of an independent electrical connection test terminal  180  illustrated in  FIGS. 10A-C  and  11  can also be implemented in the electrical connection system described with reference to  FIGS. 1-7 . For example an independent connection test terminal can be provided in electrical connector plug  20 . 
     In accordance with embodiments described herein, portable electrical energy storage devices can be removably received by receptacles for the portable electrical energy storage devices. In  FIGS. 1 and 8  electrical connectors  16  and  126  are illustrated as part of portable electrical energy storage devices  12  and  122 , respectively. The same figures illustrate electrical connector plugs  20  and  128  as part of portable electrical energy storage device receptacles  18  and  128 , respectively. Embodiments described herein are not limited to electrical connectors  16  or  126  being part of portable electrical energy storage devices. For example, electrical connectors  16  and  126  may be part of receptacles  18  or  128  for receiving portable electrical energy storage devices. When receptacles  18  or  128  include electrical connectors  16  or  126 , portable electrical energy storage devices  12  or  122  will include the counterpart electrical connector plug  20  or  128 . 
     An advantage of an electrical connection system including the electrical connector and electrical connection plug in accordance with embodiments described herein is the ability to establish an electrical connection between a portable electrical energy storage device and a device to be powered by or for charging the portable electrical energy storage device in a plurality of rotational orientations and, in the embodiments of  FIGS. 1-8 , an infinite number of rotational orientations. In accordance with embodiments described herein, a multidirectional or omni-directional electrical connection system is provided whereby electrical connection between an electrical connector and an electrical connection plug can be established in a plurality of rotational orientations and in some cases in an infinite number of rotational orientations. The ability to make electrical connections in a plurality or infinite number of rotational orientations reduces the likelihood of a faulty electrical connection due to a user inserting a battery pack into a battery pack receptacle in an improper rotational orientation. Electrical connections between a device including an electrical connector and a device including an electrical connector plug in accordance with embodiments described herein can be made when the devices are mated with each other in a plurality of rotational orientations. The ability to make electrical connections in a plurality of rotational orientations has other advantages, such as reducing the likelihood that damage will be done to the electrical connector or electrical connector plug due to the portable electrical energy storage device being inserted into the receptacle in an orientation in which an electrical connection cannot be made between the electrical connector and electrical connection plug or an orientation in which the electrical connector and electrical connection plug cannot mate physically with each other. 
     In accordance with additional embodiments of the subject matter described herein, multidirectional electrical connection systems capable of establishing an electrical connection between a portable electrical energy storage device and a device to be powered by or for charging the portable electrical energy storage device in a plurality of rotational orientations include electrical terminal patterns such as those illustrated in  FIGS. 12-14 . 
     Referring to  FIGS. 12A-12C ,  FIG. 12A  is a schematic illustration of a top of a receptacle  184  for receiving a portable electrical energy storage device  194  and making electrical connection between electrical terminals of the receptacle and electrical terminals of a portable electrical energy storage device in two different rotational orientations of the portable electrical energy storage device  194  relative to receptacle  184 . More specifically,  FIG. 12A  is a top down schematic illustration of the bottom of a receptacle  184  for receiving a portable electrical energy storage device (not shown). In the illustrated embodiment, the bottom of receptacle  184  includes two positive electric terminals  186  arranged in a horizontal row and two negative terminals  188  arranged in a horizontal row below positive electric terminals  186 .  FIG. 12B  illustrates an arrangement of a positive terminal  190  and a negative terminal  192  located on the bottom of a portable electrical energy storage device  194  that has been received by receptacle  184  in a first rotational orientation. In this exemplary embodiment, positive terminal  190  is located in an opposite corner of portable electrical energy storage device  194  from negative terminal  192 . Dotted line  196  identifies the outline of receptacle  184 . Dotted lines  198  and  200  identify positive terminals  186  and negative terminals  188  of receptacle  184 .  FIG. 12C  illustrates the position of positive terminal  190  and negative terminal  192  after portable electrical energy storage device  194  is rotated counterclockwise by 90°, placing portable electrical energy storage device  194  in a second rotation orientation relative to receptacle  184 . 
       FIG. 13A  is a schematic illustration of a different configuration of electrical terminals in a receptacle  184  for receiving a portable electrical energy storage device  194  and electrical terminals on the portable electrical energy storage device for making electrical connection between the receptacle and the portable electrical energy storage device in two different rotational orientations. More specifically,  FIG. 13A  is a top down schematic illustration of the bottom of a receptacle  184  for receiving a portable electrical energy storage device (not shown). In the illustrated embodiment, the bottom of receptacle  184  includes two positive electric terminals  186  and two negative electric terminals  188 . Positive electric terminals  186  are located in opposite corners of the receptacle and negative terminals  188  are located in the remaining opposing corners.  FIG. 13B  illustrates an arrangement of a positive terminal  190  and a negative terminal  192  located on the bottom of a portable electrical energy storage device  194  that has been received by receptacle  184 . In this exemplary embodiment, positive terminal  190  is located in a corner of portable electrical energy storage device  194  above a corner occupied by negative terminal  192 . Dotted line  196  identifies the outline of receptacle  184 . Dotted lines  198  and  200  identify positive terminals  186  and negative terminals  188  of receptacle  184  respectively.  FIG. 13C  illustrates the position of positive terminal  198  and negative terminal  192  after portable electrical energy storage device  194  has been rotated counterclockwise by 180°. In this manner, receptacle  184  and portable electrical energy storage device  194  cooperate so that an electrical connection between the electrical terminals of receptacle  184  and the electrical terminals of portable electrical energy storage device  194  can be made in two different rotational orientations of the receptacle  184  relative to the portable electrical energy storage device  194 . 
       FIG. 13D  illustrates another arrangement of a positive terminal  190  and a negative terminal  192  located on the bottom of a portable electrical energy storage device  194  that has been received by receptacle  184 . In  FIG. 13D , the arrangement of positive terminals  186  and negative terminals  188  at the bottom of receptacle  184  are the same as described and illustrated in  FIGS. 13A-13C . In this exemplary embodiment, positive terminal  190  is located in a corner of portable electrical energy storage device  194  adjacent a corner occupied by negative terminal  192 . Dotted line  196  identifies the outline of receptacle  184 . Dotted lines  198  and  200  identify positive terminals  186  and negative terminals  188  of receptacle  184 .  FIG. 13E  illustrates the position of positive terminal  190  and negative terminal  192  after portable electrical energy storage device  194  has been rotated counterclockwise 180°. In this manner, receptacle  184  and portable electrical energy storage device  194  cooperate so that an electrical connection between the electrical terminals of receptacle  184  and the electrical terminals of portable electrical energy storage device  194  can be made in two different rotational orientations of the receptacle  184  relative to the portable electrical energy storage device  194 . 
     Though not illustrated, electrical connections between the receptacle  184  and portable electrical energy storage device  194  illustrated in  FIGS. 12A-12C and 13A-13D  in at least two rotational orientations can also be achieved if the illustrated arrangement of positive and negative terminals at the bottom of receptacle  184  are provided on the bottom of portable electrical energy storage device  194  and the arrangement of positive and negative terminals at the bottom of portable electrical energy storage device  194  are provided at the bottom of receptacle  184 . 
     In contrast to the embodiments illustrated in  FIGS. 12A-12C and 13A-13E , electrical connection systems illustrated in  FIGS. 14A-14D  do not include positive terminals and negative terminals located at the same end of a portable electrical energy storage device or a receptacle for the portable electrical energy storage device, but rather positive terminals  203  are located at one end  204  of portable electronic storage device  202  and negative terminals  205  are located at an opposite end  206  of portable electrical energy storage device  202 . In the embodiment illustrated in  FIG. 14A , positive terminals  210  are located in the bottom (schematically illustrated as  208 ) of a receptacle for receiving portable electrical energy storage device  202 . The top of the receptacle (schematically illustrated as  212 ) includes four negative terminals  214 . With the arrangement of positive terminals  203  and negative terminals  205  on portable electrical energy storage device  202  shown in  FIG. 14A  and the arrangement of positive terminals  210  and negative terminals  214  at the bottom and top of the receptacle for receiving portable electrical energy storage device  202  shown in  FIG. 14A , the portable electrical energy storage device  202  can be received into the receptacle in at least four different rotational orientations relative to the receptacle.  FIGS. 14B-14D  illustrate further arrangements of positive electrical terminals  203  on the bottom of portable electrical energy storage device  202  and arrangement of negative electrical terminals  205  on the top of portable electrical energy storage device  202 . In  FIG. 14B , two negative terminals  205  are located along one edge of the top end  206  of portable electrical energy storage device  202  and two positive electrical terminals are located along the same edge of the bottom end  204  of portable electrical energy storage device  202 . In accordance with embodiments of the subject matter described herein, the pair of negative electrical terminals  205  need not be positioned along the same edge as the pair of positive electrical terminals  203 . For example, the pair of positive electrical terminals  203  can be positioned along an edge of portable electrical energy storage device  202  that is opposite the edge along which negative terminals  205  are located or adjacent the edge along which negative terminals  205  are located.  FIG. 14C  illustrates embodiments in accordance with the present disclosure that include a pair of negative terminals  205  located in opposite corners of the top end  206  of portable electrical energy storage device  202  and a pair of positive terminals  203  located in the same opposite corners of the bottom end  204  of portable electrical energy storage device  202 . In accordance with embodiments of the subject matter described herein, the pair of negative electrical terminals  205  need not be located in the same opposite corners as the pair of positive electrical terminals  203 . For example, the pair of negative electrical terminals  205  can be located in unoccupied opposing corners of the top  206  of portable electrical energy storage device  202 . 
       FIG. 14D  illustrates embodiments in accordance with the present disclosure that include a single negative terminal  205  located in a corner of the top end  206  of portable electrical energy storage device  202  and a single positive terminal  203  located in the same corner of the bottom end  204  of portable electrical energy storage device  202 . In accordance with embodiments of the subject matter described herein, negative electrical terminal  205  need not be located in the same corner as the positive electric terminals  203 . For example, negative electrical terminal  205  can be located in an unoccupied corner of the top  206  of portable electrical energy storage device  202 . 
     In  FIGS. 14A-14D , fewer negative electrical terminals  214  can be provided at the top  212  of the receptacle for portable electrical energy storage device  202  and fewer positive electrical terminals  210  can be provided at the bottom  208  of the receptacle for portable electrical energy storage device  202 . Such negative electrical terminals  214  and positive electrical terminals  210  can be provided at numerous locations, provided such locations cooperate with the locations of negative terminals  205  and positive terminals  203  of portable electrical energy storage device  202  and provide for making an electrical connection between the terminals of the receptacle and the terminals of the portable electrical energy storage device  202  in more than one rotational orientation of portable electrical energy storage device  202  relative to the receptacle. 
     While the embodiments of  FIGS. 12A-12C, 13A-13E and 14A-14D  have been described with reference to specific locations of the positive terminals and negative terminals relative to the portable electrical energy storage device and the receptacle for the portable electrical energy storage device, in accordance with embodiments of the present disclosure, the locations of the positive electrical terminals and the negative electrical terminals relative to the portable electrical energy storage device and the receptacle for the portable electrical energy storage device can be reversed. For example, described arrangements of positive electric terminals and negative electric terminals on a portable electrical energy storage device can alternatively be provided on the receptacle for the portable electrical energy storage device and described arrangements of positive electric terminals and negative electric terminals on the receptacle can be provided on the portable electrical energy storage device. 
     Details of another embodiment of the present disclosure are described below with reference to  FIGS. 15-18, 19A-19C and 20-23 .  FIGS. 15-16  illustrate one exemplary embodiment of an electrical connector  326  electrically connected to a portable electrical energy storage device or to a device to be powered by or for charging the portable electrical energy storage device and an electrical connector plug  328  connected to a portable electrical energy storage device or to a device to be powered by or for charging the portable electrical energy storage device that is not connected to the electrical connector  326 . Electrical connector  326  in the illustrated exemplary embodiment includes an electrically nonconductive connector base  336 , a first electrically conductive terminal  338 , a second electrically conductive terminal  340 , an electrical connection test terminal  342  and a resilient electrically conductive connector  343 . 
     Electrically nonconductive connector base  336  includes a connector base outer wall  344 . In the illustrated exemplary embodiment of  FIGS. 15 and 16, 19A-19C and 20 , electrically nonconductive connector base  336  is circular in shape when viewed along its longitudinal axis  347 . The electrically nonconductive connector base  336  including connector base outer wall  344  is formed of a nonconductive material, such as plastic. Conventional techniques such as extrusion or injection molding can be used to form nonconductive connector base  336  and connector base outer wall  344 . Electrically nonconductive connector base  336  further includes an annular shaped electrical contact housing  346  that includes an inner surface  348  and an outer surface  350 . Electrical contact housing  346  is formed out of an electrically nonconductive material, such as an electrically nonconductive plastic. In the illustrated embodiment, the electrical contact housing  346  is integral with the electrically nonconductive connector base  336 . Thus, in the illustrated embodiment, electrically nonconductive connector base  336  including connector base outer wall  344  and electrical contact housing  346  is an integral element; however, electrically nonconductive connector base  336  need not be an integral element, for example, conductive base outer wall  344  and electrical contact housing  346  can be formed separately and attached to each other. In the exemplary embodiment illustrated in  FIG. 15 , annular shaped electrical contact housing  346  is a round when viewed in cross-section along longitudinal axis  347 . Annular shaped electrical contact housing  346  can be polygonal shaped and not round when viewed in cross-section along longitudinal axis  347 . For example, electrical contact housing  346  can have the shape of a rectangle, pentagon, hexagon, heptagon, octagon or other polygon with more than eight sides. Inner surface  348  of the electrical contact housing  346  is located closer to longitudinal axis  347  than outer surface  350  of the electrical contact housing  346 . Outer surface  350  of the electrical contact housing  346  is separated from connector base inner wall  345  by an electrically nonconductive medium, such as air or other electrically nonconductive medium, such as a nonconductive plastic. 
     Inner surface  348  of electrical contact housing  346  includes first electrically conductive terminal  338 . In the illustrated exemplary embodiment, first electrically conductive terminal  338  is a ring-shaped member conforming to the shape of the inner surface  348  of the electrical contact housing  346 . First electrically conductive terminal  338  is in electrical contact with a resilient connector  343 A. Resilient connector  343 A is a spring-like member that can be compressed in a lateral direction perpendicular to longitudinal axis  347 . The compressive characteristic of the described resilient connectors allows electrical connector plug  328  to be inserted into electrical connector  326  and achieving low resistance, electrical connection between first electrical terminal  338  and electrical terminal  364  of electrical connector plug  328 . Resilient connector  343 A is electrically conductive and of low electrical resistance. In addition, resilient connector  343 A is resistant to corrosion or other degradation that could negatively affect its electrical conductivity and/or electrical resistance. In the illustrated embodiment, resilient connector  343 A is illustrated as what is known as a crown spring connector. While an embodiment of a resilient connector has been illustrated with reference to a crown spring connector, resilient connectors which are not crown spring connectors are included in embodiments of the resilient connectors described herein. One exemplary embodiment of a resilient connector  343  is illustrated in  FIGS. 17 and 18 . In the illustrated embodiment, first electrically conductive terminal  338  is electrically connected at its base to a first terminal connector  354 . First terminal connector  354  can be electrically connected to a portable electrical energy storage device or a device to be powered by or for charging the portable electrical energy storage device, thus providing an electrical connection between the portable electrical energy storage device or the device to be powered by or for charging the portable electrical energy storage device and the first electrically conductive terminal  338 . 
     Outer surface  350  of electrical contact housing  346  includes a second electrical conductive terminal  340 . In the illustrated exemplary embodiment, second electrical conductive terminal  340  is a ring-shaped member conforming to the shape of outer surface  350  of the electrical contact housing  346 . In the exemplary embodiment illustrated in  FIGS. 15 and 16 , second electrically conductive terminal  340  is ring-shaped when viewed in cross-section along axis  347 . Second electrically conductive terminal  340  is electrically connected at its base to a second terminal connector  358 . Second terminal connector  358  can be electrically connected to a portable electrical energy storage device or a device to be powered by or for charging a portable electrical energy storage device, thus providing an electrical connection between the portable electrical energy storage device or the device to be powered by or for charging the portable electrical energy storage device and the second electrically conductive terminal  340 . In order to avoid obscuring aspects of the subject matter described herein, details of how first terminal connector  354  and second terminal connector  358  are electrically connected to a portable electrical energy storage device or an electrically powered device are omitted. In the illustrated embodiment, tops of first electrically conductive terminal connector  338  and second electrically conductive terminal connector  340  are bridged by an electrically non-conductive cap  341 . 
     In the exemplary embodiment illustrated in  FIGS. 15 and 16 , electrical connection test terminal  342  of electrical connector  326  is an electrically conductive member in the shape of a cylinder centered along longitudinal axis  347 . Electrical connection test terminal  342  is positioned radially inward of first electrically conductive terminal  338 . The upper surface of electrical connection test terminal  342  is recessed below the upper surfaces of conductive base outer wall  344 , electrical contact housing  346 , first electrically conductive terminal  338  and second electrically conductive terminal  340 . Electrical connection test terminal  342  is electrically connected to connection test terminal connector  360 . In the illustrated embodiment, electrical connection test terminal  342  is electrically connected to connection test terminal connector  360  at its bottom; however, electrical connection between electrical connection test terminal  342  and connection test terminal connector  360  need not be at the bottom of connection test terminal  342 . Connection between connection test terminal  342  and electrical connection test terminal connector  360  can occur at different locations along the body of electrical connection test terminal  342 . 
     Referring to  FIGS. 19A-19C and 20 , an exemplary electrical connector plug  328  in accordance with embodiments described herein is illustrated. Electrical connector plug  328  includes a nonconductive plug housing  362 , a first electrical terminal  364  and a second electrical terminal  366 . The first electrical terminal  364  and second electrical terminal  366  are sized and shaped to mate with the electrical connector  326  and its respective components. When mated, electrical connection is made between electrical connector  326  and electrical connector plug  328 . In the illustrated embodiments, first electrical terminal  364  and second electric terminal are provided with resilient connector  343 C and  343 B respectively. 
     Nonconductive plug housing  362  includes a plug body  370  comprising an electrically nonconductive material, such as an electrically nonconductive plastic. Plug body  370  has a cylindrical shape and is centered along plug housing longitudinal axis  368 . From one end of plug body  370  (the top end in  FIG. 19A ), first electrical terminal  364  and a second electrical terminal  366  protrude. First electrical terminal  364  and second electrical terminal  366  are formed out of an electrically conductive material, such as an electrically conductive metal. At the end of plug body  370  where first electrical terminal  364  and second electrical terminal  366  protrude, an annular terminal housing  372  protrudes from plug body  370  beyond the ends of first electrical terminal  364  and second electrical terminal  366 . In the embodiment illustrated in  FIG. 19A , annular terminal housing  372 , when viewed along longitudinal axis  368 , has a round shape; however, the shape of annular terminal housing is not limited to a round shape. For example, when the shape of the gap between outer surface  350  of electrical contact housing  346  and conductor-base inner wall  345  of connector  326  in  FIG. 15  is something other than round, annular terminal housing  372  will have a complementary non-round shape. For example, if the shape of the gap between the outer surface  350  of the electrical contact housing  346  and conductor base inner wall  345  is square, annular terminal housing  372  will have a complementary square shape and will be sized to be received into that gap. One of the reasons the shapes are complementary is so annular terminal housing  372  can be received into the gap between outer surface of second electrical terminal  340  and inner surface  345  of electrical contact housing  346 , thus allowing connector  326  and plug  328  to mate with each other. 
     At the end of annular terminal housing  372  adjacent nonconductive plug body  370  (the bottom end in  FIG. 19A ), first terminal connector  374  of first electrical terminal  364  and second terminal connector  375  of second electrical terminal  366  protrude from annular terminal housing  372 . Alternatively, first terminal connector  374  and second terminal connector  375  do not protrude from annular terminal housing  372 , but rather are accessible within terminal housing body  372 . In  FIG. 19B  the interior of nonconductive plug body  370  is shown as being hollow. In accordance with other embodiments described herein, nonconductive plug body  370  is filled with a nonconductive material, such as a nonconductive plastic, and the first terminal connector  374  and second terminal connector  375  extend through and protrude from this nonconductive material at an end of the nonconductive plug body  370  that is opposite annular electrical terminal housing  372 . First terminal connector  374  and second terminal connector  375  provide electrical connectors for making an electrical connection with first electrical terminal  364  and second electrical terminal  366 . First terminal connector  374  and second terminal connector  375  are electrically connected to electrical cables  379  and  377  respectively. Cables  377  and  379  may be electrically connected to a portable electrical energy storage device or an electrically powered device. 
     In the embodiment illustrated in  FIGS. 19A-19C , first electrical terminal  364  is formed out of an electrically conductive material, such as a conductive metal. When viewed along longitudinal axis  368 , first electrical terminal  364  has an annular round shape and includes a cylindrical bore centered on longitudinal axis  368  that passes through first electrical terminal  364 . First electrical terminal  364  is in electrical contact with a resilient connector  343 C. Resilient connector  343 C is a spring-like member that can be compressed in a lateral direction perpendicular to longitudinal axis  368 . Resilient connector  343 C is similar to resilient connector  343 A described above. Resilient connector  343 C is smaller in diameter and length than resilient connector  343 A. The compressive characteristic of the described resilient connector  343 C allows test connection terminal  342  to be inserted into electrical connector plug  328  and achieve low resistance, electrical connection between test connection terminal  342  and first electrical terminal  364  of electrical connector plug  328 . One exemplary embodiment of a resilient connector  343  is illustrated in  FIGS. 17 and 18 . First electrical terminal  364  may have a shape other than the illustrated round shape, for example, first electrical terminal  364  can have a square shape when viewed along longitudinal axis  368  or it can have a polygon shape other than a square, for example, a triangle, rectangle, pentagon, hexagon, octagon, or a polygon having more than eight sides. Preferably, first electrical terminal  364  has a shape that complements the shape of the electrical contact housing  346  of electrical connector  326  in  FIG. 15 . When the shape of first electrical terminal  364  complements the shape of the electrical contact housing  346  (e.g., the shape of first electrical terminal  364  and the shape of electrical contact housing  346  are related in a male plug/female receptacle relationship), first electrical connection terminal  364  can be received in electrical contact housing  346  and the two are able to mate with each other. 
     In the exemplary embodiment illustrated in  FIGS. 19A-19C , an inner surface of annular electrical terminal housing  372  includes a second electrical connection terminal  366 . Second electrical terminal  366  is formed out of an electrically conductive material, such as an electrically conductive metal. As illustrated in  FIG. 19C , second electrical terminal  366  is round when viewed in cross-section perpendicular to central axis  368 . While the exemplary embodiment of  FIGS. 19A-19C  illustrate a round second electrical terminal  366 , second electrical terminal  366  is in electrical contact with a resilient connector  343 B. Resilient connector  343 B is a spring-like member that can be compressed in a lateral direction perpendicular to longitudinal axis  347 . Resilient connector  343 B is similar to resilient connector  343 A and  343 C described above. Resilient connector  343 B is larger in diameter and length than resilient connectors  343 A and  343 C. The compressive characteristic of the described resilient connector  343 B allows connector plug  328  to be inserted into electrical connector  326  and achieve low resistance, electrical connection between electrical terminal  340  and second terminal  366 . One exemplary embodiment of a resilient connector  343  is illustrated in  FIGS. 17 and 18 . 
     Second electrical terminal  366  may have a shape other than the illustrated round shape, for example, second electrical terminal  366  can have a square shape when viewed along longitudinal axis  368  or it can have a polygon shape other than a square, for example, a triangle, rectangle, pentagon, hexagon, octagon, or a polygon having more than eight sides. Preferably, second electrical terminal  366  has a shape that complements the shape of the gap between inner wall  345  of non-conductive connector base  336  and the outer surface of second electrical connector  340  in  FIG. 15 . In the embodiment illustrated in  FIG. 19A-19C , first electrical terminal  364  and second electrical terminal  366  extend through the end of electrical terminal housing  372  adjacent nonconductive plug body  370 . Located adjacent inner surface of annular electrical terminal housing  372  is a connection test terminal  380 . Connection test terminal  380  is an electrically conductive material such as an electrically conductive metal. In the embodiment illustrated in  FIGS. 19A-19C , connection test terminal  380  extends from an end of annular electrical terminal housing  372  adjacent nonconductive plug body  370 . This protruding end of connection test terminal  380  provides an electrical connector  382  for making an electrical connection between electric cable  383  and connection test terminal  380 . In the illustrated embodiment, connection test terminal  380  includes a biased tab  381 . Connection test terminal  380  and biased tab  381  are described in more detail below with reference to  FIGS. 21-23 . 
     In the embodiment illustrated in  FIGS. 21-23  another embodiment of a connection test terminal is shown. The embodiment illustrated in  FIGS. 21-23  includes connection test terminal  380  and connection test terminal housing  385 . Connection test terminal  380  is an elongate conductive metal strip. At one end of connection test terminal  380  is located a connection test terminal tab  381  and disconnect bearing surface  386 . At the opposite end of connection test terminal  380  is connection terminal  382 . Connection test terminal tab  381  is a resilient member biased in a direction towards longitudinal axis  368  of connector plug  328 . Connection test terminal tab  381  is a resilient, electrically conductive material such as an electrically conductive metal. In the illustrated embodiment, connection test terminal tab  381  is formed by removing a portion of the metal strip around three sides of connection test terminal tab  381  while not removing metal along one short edge of the metal strip. Bending the connection test terminal tab  381  along the portion of the metal strip that has not been removed and towards the longitudinal axis  368  causes connection test terminal tab  381  to be biased in an inward direction. In the illustrated embodiment, below connection test terminal tab  381 , test connection terminal  380  includes a disconnect bearing surface  386 . In the illustrated embodiment, disconnect bearing surface  386  is provided by an additional strip of metal bent outward slightly to form a surface that preferably does not snag or catch on outer surface  340  of electrical connector  326  when electrical connector plug  328  is disengaged from electrical connector  326 . In the illustrated embodiment, the metal strip forming disconnect bearing surface  386  is bent at approximately 10 to 45 degrees relative to connection test terminal tab  381 . The resiliency and bias of test connection terminal  380  serves to maintain test connection terminal  380  in contact with outer surface  340  of electrical connector  326 . The bearing surface of connection test terminal tab  381  causes test connection terminal  380  to be pushed away from longitudinal axis  368  when electrical connection plug is inserted into electrical connector  326 . 
     Connection test terminal tab  381  in the illustrated embodiment is housed within a connection test terminal housing  385 . Connection test terminal housing  385  is formed from a nonconductive material, such as plastic and is received into a cut out  387  formed in second electrical terminal  366 . Cut out  387  is sized to meet him closely with connection test terminal housing  385 . By positioning connection test terminal  380  within connection test terminal housing  385 , connection test terminal  380  is electrically isolated from second conductive terminal  366 . Connection test terminal housing  385  includes a cut out  389  sized to allow connection test terminal tab  381  to be exposed when connection test terminal  380  is positioned within connection test terminal housing  385 . Annular terminal housing  372  also includes a void  390  sized and shaped to receive and retain connection test terminal housing  385 .  FIG. 21-23  illustrate an exemplary embodiment of the connection test terminal housing  385 ; however, it is understood that connection test terminals of different sizes are also encompassed by the embodiments described herein. 
     First terminal connector  374  and second terminal connector  375  provide electrical connection points for connecting first electrical terminal  364  and second electrical terminal  366  to a portable electrical energy storage device or to a device to be powered by or for charging the portable electrical energy storage device. 
     Referring to  FIG. 20 , electrical connector  326  of  FIGS. 15 and 16  and electrical connector plug  328  of  FIGS. 19A-19C  are illustrated in a mated configuration. In this mated configuration, first electrical terminal  338  of electrical connector  326  makes electrical contact with first electrical terminal  364  of the electrical connector plug  328  via resilient connector  343 A located intermediate first electrical terminal  338  and first electrical terminal  364 . Second electrical terminal  340  of electrical connector  326  makes electrical contact with second electrical terminal  366  of electrical connector plug  328  via resilient connector  343 B located intermediate second electrical terminal  340  and second electric terminal  366 . As a result, a portable electrical energy storage device or a device to be powered by or for charging such portable electrical energy storage device that is connected to electrical connector  326  is electrically connected to a portable electrical energy storage device or a device to be powered by or for charging such portable electrical energy storage device that is connected to electrical connector plug  328 . 
     In a manner similar to that described with reference to  FIG. 8 , the size and shape of electrical connector  326  and the complementary size and shape of electrical connector plug  328  permit a user to insert a battery pack into a battery pack receptacle in a plurality of rotational orientations relative to each other, while establishing a useful and safe electrical connection between the electrical connector  326  and the electrical connector plug  328 . 
     As seen in  FIG. 20 , when electrical connector  326  is mated with electrical connector plug  328 , electrical connection test terminal  342  of electrical connector  326  makes electrical contact with first electrical terminal  364  of electrical connector plug  328 . When electrical connector  326  is mated with electrical connector plug  328 , electrical connection test terminal  380  of electrical connector plug  328  makes electrical contact with second electrical terminal  340  of electrical connector  326 . Electrical connection test terminal  380  is electrically connected to one terminal of a voltage sensor (not shown) via electrical connector  382  for connection test terminal  380 . When electrical connector  326  is mated with electrical connector plug  328 , electrical connection test terminal  342  of electrical connector  326  makes electrical contact with first electrical terminal  364  of electrical connector plug  328 . Electrical connection test terminal  342  of electrical connector plug  328  is electrically connected to another terminal of the voltage sensor (not shown) via electrical connection test terminal connector  360  for connection test terminal  342 . When electrical connection test terminal  380  contacts second electrical terminal  340  and electrical connection test terminal  342  contacts first electrical terminal  364 , electrical connection test terminal  380  will be at the same voltage as second electrical terminal  340  and electrical connection test terminal  342  will be at the same voltage as first electrical terminal  364 . The voltage sensor is configured to detect the voltage between electrical connection test terminal  380  and electrical connection test terminal  342 . Comparison of this detected voltage to the voltage of the portable electrical energy storage device to which electrical connector  326  or electrical connector plug  328  are connected provides an indication of whether an electrical contact has been established between first electrical terminal  364  of electrical connector plug  328  and first electrical terminal  338  of electrical connector  326  and second electrical terminal  366  of electrical connector plug  328  and second electrical terminal  340  of electrical connector  326 . Electrical connection between these terminals will be indicated by the voltage detected by the voltage sensor being substantially equal to the voltage of the portable electrical energy storage device. The configuration of an independent electrical connection test terminal  380  illustrated in  FIGS. 19A-C  and  21 - 23  can also be implemented in the electrical connection system described with reference to  FIGS. 1-14 . For example an independent connection test terminal can be provided in electrical connector plug  20 . 
     An advantage of an electrical connection system including the electrical connector and electrical connection plug in accordance with embodiments described herein is the ability to establish an electrical connection between a portable electrical energy storage device and a device to be powered by or for charging the portable electrical energy storage device in a plurality of rotational orientations and, in the embodiments of  FIGS. 1-8  and  FIGS. 15-23 , an infinite number of rotational orientations. In accordance with embodiments described herein, a multidirectional or omni-directional electrical connection system is provided whereby electrical connection between an electrical connector and an electrical connection plug can be established in a plurality of rotational orientations and in some cases in an infinite number of rotational orientations. The ability to make electrical connections in a plurality or infinite number of rotational orientations reduces the likelihood of a faulty electrical connection due to a user inserting a battery pack into a battery pack receptacle in an improper rotational orientation. Electrical connections between a device including an electrical connector and a device including an electrical connector plug in accordance with embodiments described herein can be made when the devices are mated with each other in a plurality of rotational orientations. The ability to make electrical connections in a plurality of rotational orientations has other advantages, such as reducing the likelihood that damage will be done to the electrical connector or electrical connector plug due to the portable electrical energy storage device being inserted into the receptacle in an orientation in which an electrical connection cannot be made between the electrical connector and electrical connection plug or an orientation in which the electrical connector and electrical connection plug cannot mate physically with each other. 
     In addition, in accordance with embodiments described herein electrical connections made between a device including an electrical connector and different device including an electrical connector plug in accordance with embodiments described herein can do so repeatedly without a significant change in the resistance of the connection that could adversely affect electrical energy delivery from the portable electrical energy storage device and/or charging of the portable electrical energy storage device. In addition, electrical connections provided between a device including an electrical connector and different device including an electrical connector plug in accordance with embodiments described herein are made with low resistance to electrical power discharge or delivery to the portable electrical energy storage device. 
     In accordance with additional embodiments of the subject matter described herein, multidirectional electrical connection systems capable of establishing an electrical connection between a portable electrical energy storage device and a device to be powered by or for charging the portable electrical energy storage device in a plurality of rotational orientations include electrical terminal patterns such as those illustrated in  FIGS. 12-14 . 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.