Abstract:
A battery pack according to an exemplary aspect of the present disclosure includes, among other things, a battery assembly, a resonant device disposed about the battery assembly, a bracket located between the battery assembly and the resonant device, and at least one modulating device located between the bracket and the resonant device.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a battery testing system and method for acoustically estimating an amount of battery cell expansion and/or pressure build up inside the battery cells of an electrified vehicle battery pack. 
       BACKGROUND 
       [0002]    The desire to reduce automotive fuel consumption and emissions is well documented. Therefore, vehicles are being developed that reduce or completely eliminate reliance on internal combustion engines. Electrified vehicles are one type of vehicle currently being developed for this purpose. In general, electrified vehicles differ from conventional motor vehicles because they are selectively driven by one or more battery powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine to drive the vehicle. 
         [0003]    A high voltage battery pack typically powers the electric machines and other electrical loads of the electrified vehicle. The battery pack typically includes a plurality of battery cells that are compressed together to a specific extent in one or more cells stacks or modules. The battery cells may expand or swell due to internal pressure build-up caused by electrolyte decomposition. Over time, this can result in battery cell degradation and associated loss of performance. 
       SUMMARY 
       [0004]    A battery pack according to an exemplary aspect of the present disclosure includes, among other things, a battery assembly, a resonant device disposed about the battery assembly, a bracket located between the battery assembly and the resonant device, and at least one modulating device located between the bracket and the resonant device. 
         [0005]    In a further non-limiting embodiment of the foregoing battery pack, the battery assembly includes a grouping of battery cells bound together by the resonant device. 
         [0006]    In a further non-limiting embodiment of either of the foregoing battery packs, the resonant device is a compression strap. 
         [0007]    In a further non-limiting embodiment of any of the foregoing battery packs, the resonant device is a compression rod. 
         [0008]    In a further non-limiting embodiment of any of the foregoing battery packs, the resonant device includes a body having a cut-out section that establishes a side string. 
         [0009]    In a further non-limiting embodiment of any of the foregoing battery packs, the side string contacts the at least one modulating device. 
         [0010]    In a further non-limiting embodiment of any of the foregoing battery packs, the resonant device, the bracket, and the at least one modulating device are metallic structures. 
         [0011]    In a further non-limiting embodiment of any of the foregoing battery packs, the at least one modulating device is a fret or a protrusion of the bracket and is configured in the shape of a cylindrical rod. 
         [0012]    In a further non-limiting embodiment of any of the foregoing battery packs, the at least one modulating device includes a first modulating device and a second modulating device mounted between the bracket and the resonant device. 
         [0013]    In a further non-limiting embodiment of any of the foregoing battery packs, a microphone and a measuring device are configured to measure a modulated acoustic response of the resonant device. 
         [0014]    In a further non-limiting embodiment of any of the foregoing battery packs, the pack includes an emitter, a receiver, and a control unit configured to control the emitter and the receiver to monitor a modulated acoustic response to the resonant device. 
         [0015]    In a further non-limiting embodiment of any of the foregoing battery packs, the bracket is contiguous with at least one battery cell of the battery assembly. 
         [0016]    A battery servicing method according to another exemplary aspect of the present disclosure includes, among other things, measuring a modulated acoustic response of a resonant device of a battery assembly of a battery pack, and servicing the battery pack if a difference between the modulated acoustic response of the resonant device and a nominal acoustic response of the resonant device exceeds a predefined threshold or tolerance value. 
         [0017]    In a further non-limiting embodiment of the foregoing battery servicing method, the method includes, prior to measuring the modulated acoustic response, exciting the resonant device to generate the modulated acoustic response. 
         [0018]    In a further non-limiting embodiment of either of the foregoing battery servicing methods, exciting the resonant device includes manually pinching or strumming the resonant device. 
         [0019]    In a further non-limiting embodiment of any of the forgoing battery servicing methods, exciting the resonant device includes transmitting an acoustic wave across the resonant device. 
         [0020]    In a further non-limiting embodiment of any of the forgoing battery servicing methods, measuring the modulated acoustic response is performed with a measuring device. 
         [0021]    In a further non-limiting embodiment of any of the forgoing battery servicing methods, measuring the modulated acoustic response is performed using a control unit mounted on-board an electrified vehicle. 
         [0022]    In a further non-limiting embodiment of any of the forgoing battery servicing methods, servicing the battery pack includes replacing a battery cell of the battery assembly. 
         [0023]    In a further non-limiting embodiment of any of the forgoing battery servicing methods, servicing the battery pack includes adjusting a tension of the resonant device. 
         [0024]    The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
         [0025]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
           [0027]      FIG. 2  illustrates a battery assembly for an electrified vehicle battery pack. 
           [0028]      FIG. 3  illustrates another exemplary battery assembly for an electrified vehicle battery pack. 
           [0029]      FIG. 4  illustrates another exemplary battery assembly for an electrified vehicle battery pack. 
           [0030]      FIG. 5  illustrates yet another exemplary battery assembly for an electrified vehicle battery pack. 
           [0031]      FIG. 6A  graphically illustrates a battery testing system according to a first embodiment of this disclosure. 
           [0032]      FIG. 6B  graphically illustrates a nominal acoustic response of a resonant device of a battery assembly. 
           [0033]      FIG. 6C  illustrates a modulated acoustic response of a resonant device of a battery assembly. 
           [0034]      FIG. 6D  illustrates another modulated response of a resonant device. 
           [0035]      FIGS. 7A and 7B  illustrate a battery testing system according to a second embodiment of this disclosure. 
           [0036]      FIG. 8  schematically illustrates an exemplary battery servicing method that includes acoustically determining an amount of battery cell expansion and/or internal pressure build-up of battery cells of a battery pack. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    This disclosure details a system and method for acoustically determining an amount of cell expansion and/or internal pressure of battery cells of an electrified vehicle battery pack. An exemplary battery testing system includes an acoustically or mechanically resonant device, which is used to bind a plurality of battery cells together in a grouping, a bracket located between the battery cells and the resonant device, and at least one modulating device located between the bracket and the resonant device. An exemplary battery servicing method includes measuring a modulated acoustic response of the resonant device, and servicing the battery pack if the absolute difference between the modulated acoustic response of the resonant device and a nominal (i.e., normal) acoustic response of the resonant device exceeds a predefined threshold or tolerance value. These and other features are discussed in greater detail in the following paragraphs of this detailed description. 
         [0038]      FIG. 1  schematically illustrates a powertrain  10  for an electrified vehicle  12 . Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEV&#39;s and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEV&#39;s), battery electric vehicles (BEV&#39;s), fuel cell vehicles, etc. 
         [0039]    In a non-limiting embodiment, the powertrain  10  is a power-split powertrain system that employs a first drive system and a second drive system. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery pack  24 . In this example, the second drive system is considered an electric drive system of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  28  of the electrified vehicle  12 . Although a power-split configuration is depicted in  FIG. 1 , this disclosure extends to any hybrid or electric vehicle including full hybrids, parallel hybrids, series hybrids, mild hybrids or micro hybrids. 
         [0040]    The engine  14 , which in one embodiment is an internal combustion engine, and the generator  18  may be connected through a power transfer unit  30 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In one non-limiting embodiment, the power transfer unit  30  is a planetary gear set that includes a ring gear  32 , a sun gear  34 , and a carrier assembly  36 . 
         [0041]    The generator  18  can be driven by the engine  14  through the power transfer unit  30  to convert kinetic energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
         [0042]    The ring gear  32  of the power transfer unit  30  may be connected to a shaft  40 , which is connected to vehicle drive wheels  28  through a second power transfer unit  44 . The second power transfer unit  44  may include a gear set having a plurality of gears  46 . Other power transfer units may also be suitable. The gears  46  transfer torque from the engine  14  to a differential  48  to ultimately provide traction to the vehicle drive wheels  28 . The differential  48  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  28 . In one embodiment, the second power transfer unit  44  is mechanically coupled to an axle  50  through the differential  48  to distribute torque to the vehicle drive wheels  28 . 
         [0043]    The motor  22  can also be employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  52  that is also connected to the second power transfer unit  44 . In one embodiment, the motor  22  and the generator  18  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  18  can be employed as motors to output torque. For example, the motor  22  and the generator  18  can each output electrical power to the battery pack  24 . 
         [0044]    The battery pack  24  is an exemplary electrified vehicle battery. The battery pack  24  may be a high voltage traction battery pack that includes a plurality of battery assemblies  25  (i.e., battery arrays or groupings of battery cells) capable of outputting electrical power to operate the motor  22  and/or other electrical loads of the electrified vehicle  12 . Other types of energy storage devices and/or output devices could also be used to electrically power the electrified vehicle  12 . 
         [0045]    In one non-limiting embodiment, the electrified vehicle  12  has two basic operating modes. The electrified vehicle  12  may operate in an Electric Vehicle (EV) mode where the motor  22  is used (generally without assistance from the engine  14 ) for vehicle propulsion, thereby depleting the battery pack  24  state of charge up to its maximum allowable discharging rate under certain driving patterns/cycles. The EV mode is an example of a charge depleting mode of operation for the electrified vehicle  12 . During EV mode, the state of charge of the battery pack  24  may increase in some circumstances, for example due to a period of regenerative braking. The engine  14  is generally OFF under a default EV mode but could be operated as necessary based on a vehicle system state or as permitted by the operator. 
         [0046]    The electrified vehicle  12  may additionally operate in a Hybrid (HEV) mode in which the engine  14  and the motor  22  are both used for vehicle propulsion. The HEV mode is an example of a charge sustaining mode of operation for the electrified vehicle  12 . During the HEV mode, the electrified vehicle  12  may reduce the motor  22  propulsion usage in order to maintain the state of charge of the battery pack  24  at a constant or approximately constant level by increasing the engine  14  propulsion. The electrified vehicle  12  may be operated in other operating modes in addition to the EV and HEV modes within the scope of this disclosure. 
         [0047]      FIG. 2  illustrates an exemplary battery assembly  25  that may be employed within an electrified vehicle battery pack, such as the battery pack  24  of the electrified vehicle  12  of  FIG. 1 , for example. The battery assembly  25  includes a plurality of battery cells  56  for supplying electrical power to various electrical loads of the electrified vehicle  12 . Although a total of six battery cells  56  is depicted in  FIG. 2 , the battery assembly  25  could employ a greater or fewer number of battery cells within the scope of this disclosure. In other words, this disclosure is not limited to the specific configuration shown in  FIG. 2 . 
         [0048]    The battery cells  56  may be stacked side-by-side along a longitudinal axis A to construct a grouping of battery cells  56 , sometimes referred to as a “cell stack.” In a non-limiting embodiment, the battery cells  56  are prismatic, lithium-ion cells. However, this disclosure is not limited to prismatic cells and could extend to cells having other geometries or designs (cylindrical, pouch, etc.) and/or other chemistries (nickel-metal hydride, lead-acid, etc.). 
         [0049]    Over time, the battery cells  56  can degrade due to cell expansion/swelling and internal pressure build-up associated with electrolyte decomposition. It is therefore desirable to monitor changes in battery cell expansion and internal pressure in order to ensure that the battery cells  56  are kept under a desired level of compression for achieving peak performance, longevity, and stability. Battery testing systems for systematically monitoring battery cell expansion and internal pressure are therefore detailed in the various embodiments described below. 
         [0050]    A battery testing system  58  associated with the battery assembly  25  is configured to acoustically determine an amount of battery cell expansion and internal pressure build-up inside the battery cells  56 . In a non-limiting embodiment, the battery testing system  58  includes a resonant device  60 , a bracket  62 , and one or more modulating devices  64 . The battery testing system  58  may additionally include a microphone  66  (e.g., an acoustic sensor) and a measuring device  68  (see, e.g.,  FIG. 6A ) or an emitter  90  and a receiver  92  (see, e.g.,  FIGS. 7A, 7B ). 
         [0051]    The resonant device  60  is disposed about the battery assembly  25 . The resonant device  60  may be wrapped around the battery assembly  25  to create a grouping of the battery cells  56  that are bound together. The resonant device  60  is under tension and thus applies a compressive force to the grouping of battery cells  56 . The compressive force applied by the resonant device  60  can change as a function of battery cell expansion and pressure build-up. 
         [0052]    In a first non-limiting embodiment, the resonant device  60  is a compression strap or band (see, e.g.,  FIGS. 2, 3, and 4 ). In a second non-limiting embodiment, the resonant device  60  is a compression rod (see, e.g.,  FIG. 5 ). The resonant device  60  functions both as a structural component (for compression) and a sensing device. The resonant device  60  could be any battery pack component that exhibits a characteristic frequency that changes when subjected to a change in tension resulting from battery cell swelling and internal pressure build-up. As discussed in greater detail below, the resonant device  60  can be excited to vibrate over its natural frequency, or more generally over its resonance frequency spectrum, thus generating a specific acoustic response that can be measured to determine an amount of battery cell expansion and pressure build-up. This information can then be used to determine whether the battery pack  24  requires servicing. 
         [0053]    In an additional non-limiting embodiment, the resonant device  60  includes a side string  70  (see, e.g.,  FIG. 4 ). The side string  70  is established by creating a cut-out section  72  in a main body  74  of the resonant device  60 , in a non-limiting embodiment. The side string  70  contacts the modulating device(s)  64 , and when excited, produces a specific resonance frequency. The side string  70  will generally experience the same variations in forces resulting from battery cell expansion as the main body  74  of the resonant device  60 . However, the side string  70  typically results in less damping when excited, and thus may produce a more accurate frequency response. Therefore, in some embodiments, the side string  70  can be used to more precisely monitor expansions and pressure variations of the battery cells  56 . 
         [0054]    The bracket  62  is positioned between the battery assembly  25  and the resonant device  60 . For example, in a non-limiting embodiment, the bracket  62  is sandwiched between the battery assembly  25  and the resonant device  60 . The bracket  62  can be located on any side of the battery assembly  25 . For example, in a first non-limiting embodiment, the bracket  62  is positioned at a longitudinal end of the battery assembly  25  such that it is contiguous with a face  76  of a single battery cell  56  (see, e.g.,  FIG. 2 ). In another non-limiting embodiment, the bracket  62  is positioned along a side of the battery assembly  25  such that it spans across and is contiguous with multiple battery cells  56  of the battery assembly  25  (see, e.g.,  FIG. 3 ). 
         [0055]    One or more modulating devices  64  are located between the bracket  62  and the resonant device  60 . In a non-limiting embodiment, one modulating device  64  is positioned near each of the opposing ends of the bracket  62 . The modulating devices  64  can be configured as cylindrical rods, although this disclosure in not limited to such a configuration. In further non-limiting embodiments, the modulating devices  64  are separate components from the bracket  62  and are mounted (e.g., glued or welded) to the bracket  62 , or could alternatively be integral components of the bracket  62 . In other non-limiting embodiments, the modulating devices  64  could be configured as a fret or even a protrusion of the bracket  62 . 
         [0056]    In yet another non-limiting embodiment, the resonant device  60 , the bracket  62 , and the modulating device  64  are all metallic components. Non-limiting examples of suitable metallic materials include steel, nickel, bronze or various metallic alloys. In another non-limiting embodiment, the resonant device  60 , the bracket  62 , and the modulating device  64  are made of a combination of metallic components and polymers, e.g., nylon. 
         [0057]    Referring now to  FIG. 6A , with continued reference to  FIGS. 2-5 , the battery testing system  58  may be employed to acoustically determine expansion and internal pressure of the battery cells  56  of the battery assembly  25 . Battery cell expansion can be indicative of an incorrect amount of tension exhibited by the resonant device  60 . In this non-limiting embodiment, the battery testing system  58  includes instrumentation that can be used by a vehicle service technician during a vehicle servicing method. In other words, the battery testing system  58  of this embodiment includes instrumentation that is at least partially separate from an electrified vehicle and is thus not part of an on-board monitoring system of the electrified vehicle. 
         [0058]    The resonant device  60  (either the main body  74  or the side string  70 ) may be mechanically excited, or vibrated, such as during a vehicle servicing event, to generate an acoustic response AR, or vibration response. In a non-limiting embodiment, mechanical excitation is achieved by pinching or strumming the resonant device  60 , such as using a finger or a tool (e.g., metallic pick). The acoustic response AR of the resonant device  60  is modulated to a specific frequency and is amplified and modulated by the assembly of the bracket  62  and the modulating devices  64 . The bracket  62  and the modulating devices  64  thus generate a strong and characteristic harmonic response upon excitation. The bracket  62  functions to evenly distribute a compressive load across the battery cells  56 , and the modulating devices  64  function to modulate the vibrating frequency/acoustic response of the resonant device  60  and amplify it by reducing damping. 
         [0059]    The acoustic response AR is sensed and converted into an audio signal by the microphone  66 . The audio signal can then be measured by the measuring device  68  to determine a frequency, and optionally an amplitude, of the acoustic response AR. In a non-limiting embodiment, the measuring device  68  is an acoustic sensor. In another non-limiting embodiment, the measuring device  68  is a sonic tension meter. Other measuring devices may also be used within the scope of this disclosure. The acoustic response AR changes as a function of battery cell pressure/expansion and tension of the resonant device  60 . The acoustic response AR thus can be used to assess an increase in the tension of the resonant device  60  due to battery cell expansion and/or internal pressure build-up. 
         [0060]      FIGS. 6B and 6C  graphically illustrate a nominal acoustic response  82  and a modulated acoustic response  80 , respectively, of the resonant device  60  upon excitation. The nominal acoustic response  82  of  FIG. 6B  is the expected acoustical response of the resonant device  60  if the battery cells  56  of the battery assembly  25  are healthy (e.g., are not exhibiting greater than acceptable amounts of expansion and internal pressure) and, thus, the resonant device  60  is under an appropriate amount of tension. The nominal acoustic response  82  may be determined during manufacturing of the battery assembly  25  (i.e., at end of manufacturing line) or during engineering development phases of the battery assembly  24 . In other words, the nominal acoustic response  82  is a pre-determined, reference value that a service technician can look-up and compare to the modulated acoustic response  80  to determine if a battery pack requires further servicing (e.g., battery cell replacement, band readjustment, etc.). 
         [0061]    The modulated acoustic response  80  of  FIG. 6C  represents the acoustic response of the resonant device  60  if one or more of the battery cells  56  of the battery assembly  25  are exhibiting relatively significant amounts of expansion and internal pressure and, thus, the resonant device  60  is under an increased amount of tension. The modulated acoustic response  80  may be compared with the nominal acoustic response  82  to determine if battery cell degradation and/or mechanical changes are likely and thus further battery pack servicing is required. For example, a significant deviation (e.g., beyond a predefined threshold or outside a tolerance window) of the frequency of the modulated acoustic response  80  compared to the frequency of the nominal acoustic response  82  indicates to the service technician that the level of battery cell expansion and internal pressure inside the battery cells  56  of the battery assembly  25  has likely increased beyond an upper limit and thus further battery pack servicing is deemed necessary. Conversely, a frequency measured below a lower limit value may indicate insufficient cell compression and prompts band readjustment (see, e.g.,  FIG. 6D , which shows a modulated acoustic response  80 - 2  indicating the resonant device  60  is under low tension). 
         [0062]    Another exemplary battery testing system  158  for acoustically monitoring expansion and internal pressure of battery cells  56  is illustrated in  FIGS. 7A and 7B . In this non-limiting embodiment, the battery testing system  158  is part of an on-board monitoring system of an electrified vehicle. Thus, the battery testing system  158  can be employed to continuously monitor a battery pack of the electrified vehicle. 
         [0063]    Like the battery testing system  58  described above, the battery testing system  158  includes a resonant device  60 , a bracket  62 , and one or more modulating devices  64 . However, in this embodiment, the battery testing system  158  additionally includes an emitter  90 , a receiver  92 , and a control unit  94 . 
         [0064]    The emitter  90  and the receiver  92  are mounted to the resonant device  60 . In a non-limiting embodiment, the emitter  90  and the receiver  92  are mounted on a side of the resonant device  60  that is opposite from the bracket  62  and the modulating devices  64 . In another non-limiting embodiment, the emitter  90  and the receiver  92  are piezoelectric transponders. 
         [0065]    The control unit  94  is in communication with both the emitter  90  and the receiver  92 . In one non-limiting embodiment, the control unit  94  is a battery energy control module (BECM). In another non-limiting embodiment, the control unit  94  is part of an overall vehicle control unit, such as a vehicle system controller (VSC). Alternatively, control unit  94  may be a dedicated controller communicating with the BECM or the VSC. The control unit  94  is programmed with executable instructions for interfacing with and operating the various components of the battery testing system  158 . The control unit  94  includes various inputs and outputs for interfacing with the various components of the battery testing system  158 . In addition, although not shown, the control unit  94  may additionally include a processing unit and non-transitory memory for executing the various control strategies and modes of the battery testing system  158 . 
         [0066]    In use, the control unit  94  may command excitation of the resonant device  60  by periodically commanding the transmission of an acoustic wave from the emitter  90  to the receiver  92  along the resonant device  60 . Under normal conditions, a nominal acoustic response  96  is received by the receiver  92  (see  FIG. 7A ). However, a change in stiffness of the resonant device  60 , such as due to battery cell expansion and/or internal pressure build-up, results in a modulated acoustic response  98  received by the receiver  92  (see  FIG. 7B ). 
         [0067]    The control unit  94  is configured with the necessary logic to monitor the acoustic response received by the receiver  92  and determine whether a difference between the modulated acoustic response  98  and the nominal acoustic response  96  is large enough to signify that battery cell degradation and/or mechanical changes are likely and thus further battery pack servicing is required. If so, the control unit  94  may communicate a “Service Required” message to the vehicle operator, such as by displaying the message on an interface display located inside the interior cabin of the electrified vehicle. In a non-limiting embodiment, the nominal acoustic response  96  is a pre-determined value that is stored in the memory of the control unit  94 , such as within a look-up table stored in the non-transitory memory, for example. The control unit  94  may be configured to perform additional battery control tasks, including but not limited to monitoring battery pack state of charge (SOC) or voltage, for example. 
         [0068]      FIG. 8 , with continued reference to  FIGS. 1-7B , schematically illustrates a battery servicing method  100  for determining whether to service a battery pack of an electrified vehicle. First, at block  102 , the resonant device  60  of a battery testing system  58 ,  158  is excited to create an acoustic response. The resonant device  60  may be excited manually (see embodiment of  FIG. 6A ) or by communicating an acoustic wave across the resonant device  60  (see embodiment of  FIGS. 7A and 7B ). 
         [0069]    Next, at block  104 , a modulated acoustic response is measured by either the measuring device  68  of the battery testing system  58  or the control unit  94  of the battery testing system  158 . The modulated acoustic response is compared with a pre-determined, nominal acoustic response at block  106  to determine whether a difference between the modulated acoustic response and the nominal acoustic response exceeds a predefined threshold or tolerance value. If NO, the battery servicing method  100  ends at block  108 . However, if YES, the battery servicing method  100  proceeds to block  110  by instructing the technician and/or vehicle operator that additional servicing tasks are necessary. Non-limiting examples of additional servicing tasks that may be performed include replacement of highly swollen battery cells, readjustment of tension of resonant device to maintain battery cells under healthy compression state, and/or replacement of defective components at the origin of the change in cell compression. 
         [0070]    Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0071]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
         [0072]    The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.