Patent Publication Number: US-2021175479-A1

Title: Battery configuration for gas engine replacement device

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/945,697, filed on Dec. 9, 2019, the entire content of which is hereby incorporated by reference. 
    
    
     FIELD 
     The present application relates to battery configurations for gas engine replacement devices. 
     BACKGROUND 
     Outdoor power equipment (e.g., lawn and garden equipment) and construction equipment (e.g., concrete mixers, plate compactors), commonly referred to as power equipment, may include a gas engine to run the equipment. However, gas engines produce emissions and are not generally adaptable for optimal performance of the power equipment. 
     SUMMARY 
     Gas engines produce emissions and are not readily configurable for particular applications of various types of equipment. Gas engine replacement devices, also referred to as powerheads, that use, for example, Lithium-ion battery packs and electric brushless motors provide several advantages over gas engines. However, the power density of gasoline is higher than current Lithium-ion battery chemistry or other widely available battery technology. As a result, battery powered gas engine replacement devices generally include limited runtime when compared to similar sized gasoline powered engines. In other words, an attached battery pack powering a gas engine replacement is prone to be fully discharged more quickly than a gas engine is to deplete its gasoline fuel supply, where the gas engine replacement with battery pack has a similar size to that of the gas engine with fuel supply. 
     Accordingly, there is a need to increase runtime of the battery powered gas engine replacement devices to, for example, provide similar runtime as gas engines. 
     One embodiment provides a gas engine replacement device including a housing and a power source having a first battery receptacle and a second battery receptacle provided on the housing. The gas engine replacement device also includes a first battery pack received in the first battery receptacle and a second battery pack received in the second battery receptacle. The gas engine replacement device includes a motor within the housing and a power switching network coupled between the motor and the first battery pack and the second battery pack. The first battery pack is coupled to the power switching network through a first switch and the second battery pack is coupled to the power switching network through a second switch. The gas engine replacement device also includes an electronic processor coupled to the first switch, the second switch, and the power switching network. The electronic processor is configured to connect the first battery pack to the power switching network and determine whether the state of charge of the first battery pack is below a predetermined threshold. The electronic processor is further configured to connect the second battery pack to the power switching network and disconnect the first battery pack from the power switching network when the state of charge of the first battery pack is below the predetermined threshold. 
     Another embodiment provides a method for increasing the runtime of a gas engine replacement device. The gas engine replacement device includes a first battery pack coupled to a power switching network through a first switch and a second battery pack coupled to the power switching network through a second switch. The method includes connecting the first battery pack to the power switching network and determining whether the state of charge of the first battery pack is below a predetermined threshold. The method also includes connecting the second battery pack to the power switching network and disconnecting the first battery pack from the power switching network when the state of charge of the first battery pack is below the predetermined threshold. 
     Another embodiment provides a gas engine replacement device including a housing and a power source having a battery receptacle and a module port provided on the housing. The gas engine replacement device also includes a first battery pack received in the battery receptacle and a battery module coupled to the module port. A second battery pack is received in the battery module. The gas engine replacement device includes a motor within the housing and a power switching network coupled between the motor and the first battery pack and the module port. The first battery pack is coupled to the power switching network through a first switch and the battery module is coupled to the power switching network through a second switch. The gas engine replacement device also includes an electronic processor coupled to the first switch, the second switch, and the power switching network. The electronic processor is configured to connect the first battery pack to the power switching network and determine whether the state of charge of the first battery pack is below a predetermined threshold. The electronic processor is further configured to connect the battery module to the power switching network and disconnect the first battery pack from the power switching network when the state of charge of the first battery pack is below the predetermined threshold. 
     Another embodiment provides a method for increasing the runtime of a gas engine replacement device. The gas engine replacement device includes a first battery pack coupled to a power switching network through a first switch and a module port coupled to the power switching network through a second switch. The module port is configured to be coupled to battery module receiving a second battery pack. The method includes connecting the first battery pack to the power switching network and determining whether the state of charge of the first battery pack is below a predetermined threshold. The method also includes connecting the battery module to the power switching network and disconnecting the first battery pack from the power switching network when the state of charge of the first battery pack is below the predetermined threshold. 
     Another embodiment provides a gas engine replacement device including a housing, a battery receptacle provided on the housing, a battery pack received in the battery receptacle, and an on-board charging circuit for charging the battery pack. The gas engine replacement device includes a motor within the housing and a power switching network coupled between the motor and the first battery pack and the second battery pack. The battery pack is coupled to the power switching network through a discharge switch and the battery pack is coupled to the on-board charging circuit through a charge switch. The gas engine replacement device also includes a power cord to provide charging power to the on-board charging circuit, and an electronic processor coupled to the discharge switch, the charge switch, and the power switching network. The electronic processor is configured to connect the battery pack to the power switching network to operate the motor and to connect the battery pack to the on-board charging circuit to charge the battery pack. 
     Other features and aspects will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a gas engine replacement device in accordance with an embodiment. 
         FIG. 2  is a plan view of the gas engine replacement device of  FIG. 1 . 
         FIG. 3  is a schematic view of the gas engine replacement device of  FIG. 1 . 
         FIGS. 4A and 4B  are perspective views of a battery pack of the gas engine replacement device of  FIG. 1 . 
         FIGS. 5A and 5B  are cross-sectional views of the battery packs of  FIGS. 4A and 4B . 
         FIG. 6  is a cross-sectional view of a battery receptacle of the gas engine replacement device of  FIG. 1 . 
         FIG. 7  is a cross-sectional view of a motor of the gas engine replacement device of  FIG. 1 . 
         FIG. 8  is a schematic view of a motor, a gear train, and a power take-off shaft of the gas engine replacement device of  FIG. 1 . 
         FIG. 9  is a block diagram of the gas engine replacement device of  FIG. 1 . 
         FIG. 10  is a perspective view of a gas engine replacement device in accordance with an embodiment. 
         FIGS. 11A and 11B  are perspective views of a gas engine replacement device in accordance with an embodiment. 
         FIG. 12  is a block diagram of a power source of the gas engine replacement device of  FIGS. 10-11B . 
         FIG. 13  is a flowchart of a method for increasing runtime of the gas engine replacement device of  FIGS. 10-12 . 
         FIG. 14  is a perspective view of a gas engine replacement device in accordance with some embodiments. 
         FIG. 15  is a block diagram of a power source of the gas engine replacement device of  FIG. 14 . 
         FIG. 16  is a flowchart of a method for increasing runtime of the gas engine replacement device of  FIGS. 14-15 . 
         FIGS. 17A and 17B  illustrate daisy-chain circuits that enable daisy-chained battery packs to power the gas engine replacement device  10 , in accordance with some embodiments. 
         FIG. 18  is a perspective view of a gas engine replacement device in accordance with some embodiments. 
         FIG. 19  is a block diagram of a power source of the gas engine replacement device of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments are explained in detail, it is to be understood that the embodiments are not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. Embodiments described herein are capable of being practiced in or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limited. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. Additionally, as used herein with a list of items, “and/or” means that the items may be taken all together, in sub-sets, or as alternatives (for example, “A, B, and/or C” means A; B; C; A and B; B and C; A and C; or A, B, and C). 
     It should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement embodiments described herein. Furthermore, and as described in subsequent paragraphs, the specific configurations illustrated in the drawings are intended as example embodiments and other alternative configurations are possible. The terms “processor” “central processing unit” and “CPU” are interchangeable unless otherwise stated. Where the terms “processor” or “central processing unit” or “CPU” are used as identifying a unit performing specific functions, it should be understood that, unless otherwise stated, those functions can be carried out by a single processor, or multiple processors arranged in any form, including parallel processors, serial processors, tandem processors or cloud processing/cloud computing configurations. 
     In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored on non-transitory computer-readable medium) executable by one or more processing units, such as a microprocessor and/or application specific integrated circuits (“ASICs”). As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components, may be utilized to implement the embodiments. 
     As shown in  FIGS. 1 and 2 , a gas engine replacement device  10  for use with a piece of power equipment includes a housing  14  with a first side  18 , a second side  22  adjacent the first side  18 , a third side  26  opposite the second side  22 , a fourth side  28  opposite the first side  18 , a fifth side  30  extending between the second and third sides  22 ,  26 , and a sixth side  32  opposite the fifth side  30 . The gas engine replacement device  10  also includes a flange  34  coupled to the housing  14  on the first side  18 , an electric motor  36  located within the housing  14 , and a power take-off shaft  38  that protrudes from the second side  22  and receives torque from the motor  36 . As explained in further detail below, in some embodiments, the power take-off shaft  38  protrudes from the first side  18  and from the flange  34 . As shown in  FIG. 3 , the gas engine replacement device  10  also includes control electronics  42  positioned within the housing  14  and including wiring and a controller  46  that is electrically connected to the motor  36 . A similar gas engine replacement device  10  is described and illustrated in U.S. patent application Ser. No. 16/551,197, filed Aug. 26, 2019, the entire content of which is incorporated herein by reference. 
     As shown in  FIGS. 1-6 , the gas engine replacement device  10  also includes a battery pack  50 - 1 ,  50 - 2  that is removably received in a battery receptacle  54  in the housing  14  to transfer current from the battery pack  50 - 1 ,  50 - 2  to the motor  36  via the control electronics  42 . The battery pack  50 - 1 ,  50 - 2  may be singularly referred to as the battery pack  50 . With reference to  FIGS. 4-6 , the battery pack  50  includes a battery pack housing  58  with a support portion  62  and a first terminal  66  that is electrically connected to a plurality of battery cells  68  supported by the battery pack housing  58 . The support portion  62  provides a slide-on arrangement with a projection/recess portion  70  cooperating with a complementary projection/recess portion  74  (shown in  FIG. 6 ) of the battery receptacle  54 . In the embodiment illustrated in  FIGS. 4-6 , the projection/recess portion  70  of the battery pack  50  is a guide rail and the projection/recess portion  74  of the battery receptacle  54  is a guide recess. A similar battery pack is described and illustrated in U.S. Patent Publication No. 2019/0006980 filed Jul. 2, 2018, the entire content of which is incorporated herein by reference. 
       FIGS. 4A and 4B  illustrate embodiments of the battery pack  50 . The battery pack  50  may include one or more cell strings each having a number (e.g.,  10 ) of battery cells  68  connected in series to provide a desired discharge output (e.g., nominal voltage (e.g., 20V, 40V, 60V, 80V, 120V) and current capacity).  FIG. 4A  illustrates a battery pack  50 - 1  having a  20 S 2 P configuration. The battery pack  50 - 1  includes two cell strings of twenty series connected cells, the cell strings being connected in parallel.  FIG. 5B  is a cross-section of the battery pack  50 - 1  of  FIG. 4A  and illustrates a first cell string  71  and a second cell string  72  separated by a partition  73  of the battery pack housing  58 .  FIG. 4B  illustrates a battery pack  50 - 2  having a  20 S 1 P configuration. The battery pack  50 - 2  includes one cell string of twenty series connected cells. In other embodiments, other combinations of battery cells are also possible.  FIG. 5A  is a cross-section of the battery pack  50 - 2  of  FIG. 4B  and illustrates a cross section of the cell string in the battery pack housing  58 . 
     In some embodiments, the battery cells  68  have a nominal voltage of up to about 80 V. In some embodiments, the battery cells  68  have a nominal voltage of up to about 120 V. In some embodiments, the battery pack  50  has a weight of up to about 6 lb. In some embodiments, each of the battery cells  68  has a diameter of up to 21 mm and a length of up to about 71 mm. In some embodiments, the battery pack  50  includes up to twenty battery cells  68 . In some embodiments, the battery cells  68  are connected in series. In some embodiments, the battery cells  68  are operable to output a sustained operating discharge current of between about 40 A and about 60 A. In some embodiments, each of the battery cells  68  has a capacity of between about 3.0 Ah and about 5.0 Ah. 
       FIG. 6  illustrates the battery receptacle  54  of the gas engine replacement device  10  in accordance with some embodiments. The battery receptacle  54  includes the projection/recess portion  74 , a second terminal  78 , a latching mechanism  82 , and a power disconnect switch  86 . The projection/recess portion  74  cooperates with the projection/recess portion  70  of the battery pack  50  to attach the battery pack  50  to the battery receptacle  54  of the gas engine replacement device  10 . When the battery pack  50  is attached to the gas engine replacement device  10 , the second terminal  78  and the first terminal  66  are electrically connected to each other. The latching mechanism  82  protrudes from a surface of the battery receptacle  54  and is configured to engage the battery pack  50  to maintain engagement between the battery pack  50  and the battery receptacle  54 . Thus, the battery pack  50  is connectable to and supportable by the battery receptacle  54  such that the battery pack  50  is supportable by the housing  14  of the gas engine replacement device  10 . In some embodiments, the battery receptacle  54  is arranged on the housing  14  in a position to create a maximum possible distance of separation between the motor  36  and the battery pack  50 , in order to inhibit vibration transferred from the motor  36  to the battery pack  50 . In some embodiments, elastomeric members are positioned on the battery receptacle  54  in order to inhibit vibration transferred from the motor  36 , via the housing  14 , to the battery pack  50 . 
     In other embodiments (not shown), the latching mechanism  82  may be disposed at various locations (e.g., on a sidewall, an end wall, an upper end wall etc., of the battery receptacle  54 ) such that the latching mechanism  82  engages corresponding structure on the battery pack  50  to maintain engagement between the battery pack  50  and the battery receptacle  54 . The latching mechanism  82  includes a pivotable actuator or handle  90  operatively engaging a latch member  94 . The latch member  94  is slidably disposed in a bore  99  of the battery receptacle  54  and is biased toward a latching position by a biasing member  100  (e.g., a spring) to protrude through a surface of the battery receptacle  54  and into a cavity in the battery pack  50 . 
     The latching mechanism  82  also includes the power disconnect switch  86  (e.g., a micro-switch) facilitating electrical connecting/disconnecting the battery pack  50  from the battery receptacle  54  during actuation of the handle  90  to withdraw the latch member  94  from the battery pack  50 . The power disconnect switch  86  may act to electrically disconnect the battery pack  50  from the gas engine replacement device  10  prior to removal of the battery pack  50  from the battery receptacle  54 . The power disconnect switch  86  is actuated when the latch member  94  is moved from the latched position (i.e., when the latch member  94  is completely within the cavity of the battery pack  50 ) to an intermediate position. The power disconnect switch  86  is electrically connected to the controller  46  and may generate an interrupt to indicate that the battery pack  50  is being disconnected from the gas engine replacement device  10 . When the controller  46  receives the interrupt, the controller  46  begins a power down operation to safely power down the control electronics  42  of the gas engine replacement device  10 . A similar latching mechanism and disconnect switch is described and illustrated in U.S. Patent Publication No. 2019/0006980, which has been incorporated herein by reference. 
     As shown in  FIG. 7 , the motor  36  includes a motor housing  96  having an outer diameter  97 , a stator  98  having a nominal outer diameter  101  of up to about  80  mm, a rotor  102  having an output shaft  106  and supported for rotation within the stator  98 , and a fan  108 . A similar motor is described and illustrated in U.S. Patent Publication No. 2019/0006980, which has been incorporated herein by reference. In some embodiments, the motor  36  is a brushless direct current motor. In some embodiments, the motor  36  has a power output of at least about 2760 W. In some embodiments, the power output of the motor  36  may drop below 2760 W during operation. In some embodiments, the fan  108  has a diameter  109  that is larger diameter  97  of the motor housing  96 . In some embodiments, the motor  36  can be stopped with an electronic clutch (not shown) for quick overload control. In some embodiments, the motor  36  has a volume of up to about 443,619 mm 3 . In some embodiments, the motor  36  has a weight of up to about 4.6 lb. The housing  14  includes an inlet vent and an outlet vent, such that the motor fan  108  pulls air through the inlet vent and along the control electronics  42  to cool the control electronics  42 , before the air is exhausted through the outlet vent. In the embodiment illustrated in  FIG. 7 , the motor  36  is an internal rotor motor, but in other embodiments, the motor  36  can be an outer rotor motor with a nominal outer diameter (i.e. the nominal outer diameter of the rotor  102 ) of up to about  80  mm. 
     With reference to  FIG. 8 , the motor  36  can transfer torque to the power take-off shaft  38  in a variety of configurations. In some embodiments, the output shaft  106  is also the power take-off shaft  38 , such that the motor  36  directly drives the power take-off shaft  38  without any intermediate gear train. For example, the motor  36  may be a direct drive high pole count motor. As shown in  FIG. 8 , in other embodiments, the gas engine replacement device  10  includes a gear train  110  that transfers torque from the motor  36  to the power take-off shaft  38 . In some embodiments, the gear train  110  can include a mechanical clutch (not shown) to discontinue the transfer of torque from the motor  36  to the power take-off shaft  38 . In some embodiments, the gear train  110  may include a planetary transmission that transfers torque from the output shaft  106  to the power take-off shaft  38 , and a rotational axis of the output shaft  106  is coaxial with a rotational axis of the power take-off shaft  38 . In some embodiments, the gear train  110  includes a spur gear engaged with the output shaft  106  of the rotor  102 , such that the rotational axis of the output shaft  106  is offset from and parallel to the rotational axis of the power take-off shaft  38 . In some embodiments, the gear train  110  includes a bevel gear, such that the rotational axis of the output shaft  106  is perpendicular to the rotational axis of the power take-off shaft  38 . In other embodiments utilizing a bevel gear, the rotational axis of the output shaft  106  is not perpendicular, parallel, or coaxial to the rotational axis of the power take-off shaft  38 , and the power take-off shaft  38  protrudes from the flange  34 . 
     In some embodiments, the gas engine replacement device  10  includes ON/OFF indicators (not shown). In some embodiments, the gas engine replacement device  10  includes a filter (not shown) to keep airborne debris out of the motor  36  and control electronics  42 . In some embodiments, the filter includes a dirty filter sensor (not shown) and a self-cleaning mechanism (not shown). In some embodiments, the motor  36  will mimic a gas engine response when encountering resistance, such as slowing down or bogging. In some embodiments, the gas engine replacement device  10  includes a heat sink  202  in the housing  14  for air-cooling the control electronics  42  ( FIGS. 1 and 2 ). In some embodiments, the gas engine replacement device  10  is liquid cooled. 
     In some embodiments, the output shaft  106  of the rotor  102  has both forward and reverse capability as further described below. In some embodiments, the forward and reverse capability is controllable without shifting gears of the gear train  110 , in comparison to gas engines, which cannot achieve forward/reverse capability without extra gearing and time delay. Thus, the gas engine replacement device  10  provides increased speed, lower weight, and lower cost. Because the gas engine replacement device  10  has fewer moving parts and no combustion system, as compared with a gas engine, it also provides additional speed, weight, and cost advantages. 
     The gas engine replacement device  10  is able to operate in any orientation (vertical, horizontal, upside down) with respect to a ground surface for a prolonged period of time, giving it an advantage over four-cycle gas engines, which can only be operated in one orientation and at slight inclines for a shorter period of time. Because the gas engine replacement device  10  does not require gas, oil, or other fluids, it can run, be transported, and be stored upside down or on any given side without leaking or flooding 
     In operation, the gas engine replacement device  10  can be used to replace a gas engine system. Specifically, the gas engine replacement device  10  can be mounted to the piece of power equipment having a second bolt pattern by aligning a first bolt pattern defined by the plurality of apertures in the flange  34  with the second bolt pattern. In some embodiments, the flange  34  may include one or more intermediate mounting members or adapters arranged between the flange  34  itself and the flange of the piece of power equipment having the second bolt pattern, such that the adapter(s) couple the flange  34  to the piece of power equipment. In these embodiments, the adapter includes both the second bolt pattern and the first bolt pattern, such that the first bolt pattern of the flange  34  aligns with the first bolt pattern of the adapter and the second bolt pattern of the adapter aligns with the second bolt pattern defined in the piece of power equipment, thereby allowing the flange  34  of the gas engine replacement device  10  to be coupled to the piece of power equipment. 
     Alternatively, the gas engine replacement device  10  can be connected to a piece of power equipment using a belt system by providing a belt that operatively connects the power take-off shaft  38  and an equipment bit. Thus, the power take-off shaft  38  of the gas engine replacement device  10  can be used to drive the equipment. 
     During operation, the housing  14  of the gas engine replacement device  10  is comparably much cooler than the housing of an internal combustion unit because there is no combustion in the gas engine replacement device  10 . Specifically, when a gas engine unit runs, the housing of the gas engine unit is  220  degrees Celsius or higher. In contrast, when the gas engine replacement device  10  runs, all of the exterior surfaces of the housing  14  are less than 95 degrees Celsius. 
       FIG. 9  illustrates a simplified block diagram of the gas engine replacement device  10  according to one example embodiment. As shown in  FIG. 9 , the gas engine replacement device  10  includes an electronic processor  302 , a memory  306 , a power source  308 , a power switching network  310 , the motor  36 , a rotor position sensor  314 , a current sensor  318 , a voltage sensor  320 , a user input device  322  (e.g., a trigger or power button), a transceiver  326 , and indicators  330  (e.g., light-emitting diodes). In some embodiments, the gas engine replacement device  10  includes fewer or additional components than those shown in  FIG. 9 . For example, the gas engine replacement device  10  may include a battery pack fuel gauge, work lights, additional sensors, kill switch, the power disconnect switch  86 , etc. In some embodiments, elements of the gas engine replacement device  10  illustrated in  FIG. 9  including one or more of the electronic processor  302 , memory  306 , power switching network  310 , rotor position sensor  314 , current sensor  318 , voltage sensor  320 , user input device  322  (e.g., a trigger or power button), transceiver  326 , and indicators  330  (e.g., light-emitting diodes) form at least part of the control electronics  42  shown in  FIG. 3 , with the electronic processor  302  and the memory  306  forming at least part of the controller  46  shown in  FIG. 3 . 
     The memory  306  includes read only memory (ROM), random access memory (RAM), other non-transitory computer-readable media, or a combination thereof. The electronic processor  302  is configured to communicate with the memory  306  to store data and retrieve stored data. The electronic processor  302  is configured to receive instructions and data from the memory  306  and execute, among other things, the instructions. In particular, the electronic processor  302  executes instructions stored in the memory  306  to perform the methods described herein. The memory  306  also stores firmware including configurable device settings of the gas engine replacement device  10 . The electronic processor  302  accesses the firmware stored in the memory  306  to control the motor  36  according to the device settings in the firmware. 
     As described above, in some embodiments, the power source  308  may include one or more battery packs  50  received in battery receptacles  54  on the housing  14 . The power source  308  may also include one or more battery modules  158  coupled to the gas engine replacement device  10 . 
     The power switching network  310  enables the electronic processor  302  to control the operation of the motor  36 . Generally, when the user input device  322  is depressed (or otherwise actuated), electrical current is supplied from the battery pack  50  to the motor  36 , via the power switching network  310 . When the user input device  322  is not depressed (or otherwise actuated), electrical current is not supplied from the battery pack  50  to the motor  36 . In some embodiments, the amount to which the user input device  322  is depressed is related to or corresponds to a desired speed of rotation of the motor  36 . In other embodiments, the amount to which the user input device  322  is depressed is related to or corresponds to a desired torque. In other embodiments, a separate input device (e.g., slider, dial, or the like) is included on the gas engine replacement device  10  in communication with the electronic processor  302  to provide a desired speed of rotation or torque for the motor  36 . 
     In response to the electronic processor  302  receiving a drive request signal from the user input device  322 , the electronic processor  302  activates the power switching network  310  to provide power to the motor  36 . Through the power switching network  310 , the electronic processor  302  controls the amount of current available to the motor  36  and thereby controls the speed and torque output of the motor  36 . The power switching network  310  may include numerous field-effect transistors (FETs), bipolar transistors, or other types of electrical switches. For instance, the power switching network  310  may include a six-FET bridge that receives pulse-width modulated (PWM) signals from the electronic processor  302  to drive the motor  36 . 
     The rotor position sensor  314 , the current sensor  318 , and the voltage sensor  320  are coupled to the electronic processor  302  and communicate to the electronic processor  302  various control signals indicative of different parameters of the gas engine replacement device  10 , the motor  36 , the power source  308 , or a combination thereof. In some embodiments, the rotor position sensor  314  includes a Hall sensor or a plurality of Hall sensors. In other embodiments, the rotor position sensor  314  includes a quadrature encoder attached to the motor  36 . The rotor position sensor  314  outputs motor feedback information to the electronic processor  302 , such as an indication (e.g., a pulse) when a magnet of a rotor of the motor  36  rotates across the face of a Hall sensor. In yet other embodiments, the rotor position sensor  314  includes, for example, a voltage or a current sensor that provides an indication of a back electro-motive force (back-emf) generated in the motor coils. The electronic processor  302  may determine the rotor position, the rotor speed, and the rotor acceleration based on the back-emf signals received from the rotor position sensor  314 , that is, the voltage or the current sensor. The rotor position sensor  314  can be combined with the current sensor  318  to form a combined current and rotor position sensor. In this example, the combined sensor provides a current flowing to the active phase coil(s) of the motor  36  and also provides a current in one or more of the inactive phase coil(s) of the motor  36 . The electronic processor  302  measures the current flowing to the motor based on the current flowing to the active phase coils and measures the motor speed based on the current in the inactive phase coils. 
     Based on the motor feedback information from the rotor position sensor  314 , the electronic processor  302  can determine the position, velocity, and acceleration of the rotor. In response to the motor feedback information and the signals from the user input device  322 , the electronic processor  302  transmits control signals to control the power switching network  310  to drive the motor  36 . For instance, by selectively enabling and disabling the FETs of the power switching network  310 , power received from the battery pack  50  is selectively applied to stator windings of the motor  36  in a cyclic manner to cause rotation of the rotor  102  of the motor  36 . The motor feedback information is used by the electronic processor  302  to ensure proper timing of control signals to the power switching network  310  and, in some instances, to provide closed-loop feedback to control the speed of the motor  36  to be at a desired level. For example, to drive the motor  36 , using the motor positioning information from the rotor position sensor  314 , the electronic processor  302  determines where the rotor magnets are in relation to the stator windings and (a) energizes a next stator winding pair (or pairs) in the predetermined pattern to provide magnetic force to the rotor magnets in a direction of desired rotation, and (b) de-energizes the previously energized stator winding pair (or pairs) to prevent application of magnetic forces on the rotor magnets that are opposite the direction of rotation of the rotor  102 . 
     The voltage sensor  320  is configured to measure the voltage of the power source  308 , which corresponds to the state of charge of the power source  308 , and provide a signal to the electronic processor  302  indicative of state of charge. In some embodiments, the voltage sensor  320  is incorporated into the power source  308  and the power source  308  (e.g., an electronic processor of the power source  308 ) communicates a signal indicative of the state of charge of the power source  308 . In the case of the power source  308  include multiple battery packs, the voltage sensor is configured to measure voltage of each pack and provide a signal indicative of the corresponding state of charge of each pack. 
     The transceiver  326  allows for communication between the electronic processor  302  and an external device  338  (e.g., a smart phone, tablet, or laptop computer) over a wired or wireless communication network  334 . In some embodiments, the transceiver  326  may comprise separate transmitting and receiving components. In some embodiments, the transceiver  326  may comprise a wireless adapter attached to the gas engine replacement device  10 . In some embodiments, the transceiver  326  is a wireless transceiver that encodes information received from the electronic processor  302  into a carrier wireless signal and transmits the encoded wireless signal to the external device  338  over the communication network  334 . The transceiver  326  also decodes information from a wireless signal received from the external device  338  over the communication network  334  and provides the decoded information to the electronic processor  302 . 
     The communication network  334  provides a wired or wireless connection between the gas engine replacement device  10  and the external device  338 . The communication network  334  may comprise a short range network, for example, a BLUETOOTH network, a Wi-Fi network or the like, or a long range network, for example, the Internet, a cellular network, or the like. 
     As shown in  FIG. 9 , the indicators  330  are also coupled to the electronic processor  302  and receive control signals from the electronic processor  302  to turn on and off or otherwise convey information based on different states of the gas engine replacement device  10 . The indicators  330  include, for example, one or more light-emitting diodes (“LEDs”), or a display screen. The indicators  330  can be configured to display conditions of, or information associated with, the gas engine replacement device  10 . For example, the indicators  330  are configured to indicate measured electrical characteristics of the gas engine replacement device  10 , the status of the gas engine replacement device  10 , the mode of the gas engine replacement device  10 , the status of the battery pack(s)  50 , etc. The indicators  330  may also include elements to convey information to a user through audible or tactile outputs. In some embodiments, the indicators  330  include an eco-indicator that indicates an amount of power being used by the load during operation. 
     The connections shown between components of the gas engine replacement device  10  are simplified in  FIG. 9 . In practice, the wiring of the gas engine replacement device  10  is more complex, as the components of a gas engine replacement device  10  are interconnected by several wires for power and control signals. For instance, each FET of the power switching network  310  is separately connected to the electronic processor  302  by a control line; each FET of the power switching network  310  is connected to a terminal of the motor  36 ; the power line from the battery pack  50  to the power switching network  310  includes a positive wire and a negative/ground wire; etc. Additionally, the power wires can have a large gauge/diameter to handle increased current. Further, although not shown, additional control signal and power lines are used to interconnect additional components of the gas engine replacement device  10 . 
     As discussed above, the gas engine replacement device  10  includes lower runtime than similar sized gas engines.  FIG. 10-18  illustrate several battery configurations of the gas engine replacement device  10  that increase the runtime of the gas engine replacement device  10 . As shown in  FIGS. 10, 11A, and 11B , multiple battery receptacles  54  may be provided on the housing  14  of the gas engine replacement device  10  to receive multiple battery packs  50 . In  FIG. 10 , the multiple battery receptacles  54  include and are individually labeled as a first battery receptacle  54 A and a second battery receptacle  54 B, and the multiple battery packs  50  include and are individually labeled as a first battery  50 A and a second battery  50 B. 
     As shown in  FIG. 10 , the battery receptacles  54  are provided on the housing  14  extending between the top (fourth side  28 ) and the side surfaces (fifth and sixth sides  30  and  32 ). A first battery receptacle  54 A extends between the fourth side  28  and the fifth side  30 , while a second battery receptacle  54 B extends between the fourth side  28  and the sixth side  32 . In some embodiments, the battery packs  50  may be received from the fourth side  28  such that the battery packs  50  slide from the top of the housing  14  downwards into the battery receptacles  54 A and  54 B. In some embodiments, the battery packs  50  may be received from the fifth side  30  and the sixth side  32  respectively such that the battery packs  50  slide from the side surfaces of the housing  14  upwards into the battery receptacles  54 A and  54 B. In other embodiments, the battery packs  50  may be received from the second side  22  and/or the third side  26  such that the battery packs  50  slide from the second side  22  to the third side  26  or vice versa into the battery receptacles  54 A and  54 B. The battery packs  50  protrude outside the housing  14  on the fourth side  28 , the fifth side  30 , and the sixth side  32 . 
     As shown in  FIGS. 11A and 11B , the housing  14  includes a first handle  150 A and a second handle  150 B that extend from the fifth side  30  to the sixth side  32 . The first handle  150 A is provided closer to the second side  22  and the second handle  150 B is provided closer to the third side  26 . The first battery receptacle  54 A and the second battery receptacle  54 B are provided between the first handle  150 A and the second handle  150 B on the fifth side  30  and the sixth side  32  respectively. The battery packs  50  are mounted from the fourth side  28  such that the battery packs  50  slide from the top of the housing  14  downwards into the battery receptacles  54 A and  54 B. The battery packs  50  are received within recesses provided on the fifth side  30  and the sixth side  32 . Accordingly, the battery packs  50  do not extend beyond the housing  14  on the fifth side  30  and the sixth side  32 . The battery packs  50  protrude beyond the top of the housing  14  on the fourth side  28 . A support  154  may be provided on the top of the housing  14  extending approximately equal to the length of a portion of the battery pack  50  that protrudes beyond the top of the housing  14 . The support  154  provides additional support for the battery packs  50  from the vibrations caused by the gas engine replacement device  10 . The battery packs  50  and the support  154  do not extend beyond the first handle  150 A and the second handle  150 B. The first handle  150 A and the second handle  150 B provide additional protection to the battery packs  50  during a drop event. 
       FIG. 12  is a simplified block diagram of the power source  308  according to one example embodiment. The power source  308  includes the first battery pack  50 A and the second battery pack  50 B and corresponds to the multiple battery pack gas engine replacement device  10  of  FIGS. 10-11B . The power switching network  310  is coupled to the first battery pack  50 A through a first switch  350  and to the second battery pack  50 B through a second switch  354 . The first switch  350  and the second switch  354  are, for example, FETs that are controlled by the electronic processor  302  to be enabled and disabled. When the first switch  350  is enabled, the first switch  350  allows current flow from the first battery pack  50 A to the power switching network  310 . When the first switch  350  is disabled, the first switch  350  blocks current flow from the first battery pack  50 A to the power switching network  310 . The second switch  354  is similarly controlled by the electronic processor  302  to allow and block current flow from the second battery pack  50 B to the power switching network  310 . 
     During operation, the electronic processor  302  may, in some embodiments, connect only one of the first battery pack  50 A and the second battery pack  50 B to the power switching network  310  at a given time during operation (except for some temporary overlap when switching between packs). The electronic processor  302  discharges the first battery pack  50 A and the second battery pack  50 B sequentially to increase the runtime of the gas engine replacement device  10 .  FIG. 13  is a flowchart of an example method  400  for increasing a runtime of the gas engine replacement device  10 . In the example illustrated, the method  400  includes connecting, using the first switch  350 , the first battery pack  50 A to the power switching network  310  (at block  404 ). The electronic processor  302  controls the first switch  350  to allow current flow from the first battery pack  50 A to the power switching network  310 . Prior to enabling the first switch  350 , the electronic processor  302  may determine whether the first battery pack  50 A is received in the first battery receptacle  54 A and whether the state of charge of the first battery pack  50 A is above a predetermined threshold. 
     The method  400  includes determining whether the state of charge of the first battery pack  50 A is below the predetermined threshold (at block  408 ). In some embodiments, the gas engine replacement device  10  includes a voltage sensor (e.g., the voltage sensor  320 ) to measure a voltage of the first battery pack  50 A and/or the second battery pack  50 B. The electronic processor  302  determines the state of charge of the first battery pack  50 A using the voltage sensor. In other embodiments, the first battery pack  50 A includes an internal voltage sensor that determines a state of charge of the first battery pack  50 A. The electronic processor  302  communicates with a battery electronic processor of the first battery pack  50 A to receive the state of charge of the first battery pack  50 A from the battery electronic processor. For example, the first battery pack  50 A provides the state of charge information to the electronic processor  302  during a group read. 
     When the state of charge of the first battery pack  50 A is above the predetermined threshold, the method  400  returns to block  404  and continues to operate the gas engine replacement device  10  using the first battery pack  50 A. When the state of charge of the first battery pack  50 A is below the predetermined threshold, the method  400  includes connecting, using the second switch  354 , the second battery pack  50 B to the power switching network  310  (at block  412 ). The electronic processor  302  controls the second switch  354  to allow current flow from the second battery pack  50 B to the power switching network  310 . Similarly as above, prior to enabling the second switch  354 , the electronic processor  302  may determine whether the second battery pack  50 B is received in the second battery receptacle  54 B and whether the state of charge of the second battery pack  50 B is above the predetermined threshold. 
     The method  400  also includes disconnecting, using the first switch  350 , the first battery pack  50 A from the power switching network  310  (at block  416 ). The electronic processor  302  controls the first switch  350  to block current flow from the first battery pack  50 A to the power switching network  310 . In the example illustrated in  FIG. 13 , connecting the second battery pack  50 B is performed before disconnecting the first battery pack  50 A. However, it should be understand that these steps may also be performed in the reverse order. That is, the electronic processor  302  may disconnect the first battery pack  50 A from the power switching network  310  before connecting the second battery pack  50 B to the power switching network  310 . Further, in some embodiments, the electronic processor  302  may disconnect the first battery pack  50 A from the power switching network  310  simultaneously with connecting the second battery pack  50 B to the power switching network  310 . 
     In some embodiments, the electronic processor  302  may activate the indicators  330  to indicate a status of a battery pack  50  to the user. For example, the electronic processor  302  may indicate that a battery pack  50  is connected, disconnected, and/or discharged using the indicators  330 . In one example, the electronic processor  302  may turn on a different indicator  330  associated with each of the above status or may light the indicator  330  associated with a battery pack  50  in different colors based on the status of the battery pack  50 . The user may then replace a depleted battery pack  50  with a fully or partially charged battery pack  50  such that the method  400  can repeat to connect the first battery pack  50 A when the second battery pack  50 B is depleted. The method  400  thereby allows a user to continuously run the gas engine replacement device  10  while changing battery packs  50  during operation. Such an application is useful, for example, when the gas engine replacement device  10  is used for pumps (requiring continuous operation), material moving carts/buggies (such that the depleted battery pack  50  may be swapped when a user is near a charger), concrete mixers, and flat concrete saws. 
       FIG. 13  is described with respect to embodiments in which, generally, the first battery pack  50 A or the second battery pack  50 B is connected to the power switching network  310  at a given time during operation of the gas engine replacement device  10 , but not both packs. In other embodiments, both battery packs  50 A and  50 B are connected to the power switching network. For example, the battery packs  50 A and  50 B may be connected in parallel to the power switching network while the state of charge of the respective packs is above the predetermined threshold. When either of the battery packs  50 A or  50 B has a state of charge that drops below the predetermined threshold, that battery pack  50 A or  50 B is disconnected from the power switching network  310  via the respective first switch  350  or second switch  354 . At this point, the gas engine replacement device  10  is powered by the remaining battery pack  50 A or  50 B that is still connected, and the user may replace the depleted battery pack  50 A or  50 B with a fully or partially charged battery pack  50 . Upon replacement, the electronic processor  302  may control the associated first switch  350  or second switch  354  to connect the newly inserted battery pack  50  to the power switching network  310 , in parallel with the battery pack  50 A or  50 B that was not removed. In another example, the battery packs  50 A and  50 B are coupled in series to the power switching network, providing a higher supply voltage for the gas engine replacement device  10 . In some embodiments of the series connected battery packs  50 A and  50 B, a single switch  350  may be provided in series with the battery packs  50 A and  50 B. Then, when either of the battery packs  50 A or  50 B has a state of charge that drops below the predetermined threshold, the switch  350  opens to disconnect both battery packs  50 A and  50 B. 
       FIG. 14  illustrates several battery modules  158  that can be daisy-chained with the battery receptacle  54  on the housing  14  of the gas engine replacement device  10 . The gas engine replacement device  10  includes a module port  162  (e.g., on the housing  14 ) to connect to one or more of the battery modules  158 . Each battery module  158  includes a module housing  164  including a module battery receptacle  166 . The module battery receptacle  166  is similar to the battery receptacle  54  on the housing  14  of the gas engine replacement device  10 , with each module battery receptacle  166  including an electrical and mechanical interface to engage a battery pack  50 . The battery packs  50  are received in the module battery receptacle  166 . The module housing  164  includes an output connector port  170  and an input connector port  174 . A first cord  178 A is used to couple a first battery module  158 A to the gas engine replacement device  10 . The first cord  178 A couples the output connector port  170  to the module port  162  to provide operating current from a first battery pack  50 A received in the first battery module  158 A to the gas engine replacement device  10 . A second cord  178 B is used to couple a second battery module  158 B to the first battery module  158 A to provide operating current from a second battery pack  50 B received in the second battery module  158 B to the first battery module  158 A. The first battery module  158 A passes the operating current from the second battery module  158 B along with the operating current from the first battery pack  50 A to the gas engine replacement device  10  through the first cord  178 A. In some embodiments, the battery module  158  can be mounted directly on to the gas engine replacement device  10  or the power equipment powered by the gas engine replacement device  10 . 
       FIG. 15  is a simplified block diagram of the power source  308  according to another example embodiment. The power source  308  includes a battery pack  50  and a module port  162  and corresponds to the gas engine replacement device  10  of  FIG. 14 . The power switching network  310  is coupled to the battery pack  50  through a first switch  350  and to the module port  162  through a second switch  354 . The module port  162  is used to connect one or more battery modules  158  to the gas engine replacement device  10 . The first switch  350  and the second switch  354  are, for example, FETs that are controlled by the electronic processor  302  to be enabled and disabled. When the first switch  350  is enabled, the first switch  350  allows current flow from the battery pack  50  to the power switching network  310 . When the first switch  350  is disabled, the first switch  350  blocks current flow from the battery pack  50  to the power switching network  310 . The second switch  354  is similarly controlled by the electronic processor  302  to allow and block current flow from the one or more battery modules  158  to the power switching network  310 . 
     During operation, the electronic processor  302  may connect only one of the battery pack  50  and the one or more battery modules  158  to the power switching network  310 . The electronic processor  302  discharges the battery pack  50  and one or more battery modules  158  sequentially to increase the runtime of the gas engine replacement device  10 .  FIG. 16  is a flowchart of an example method  430  for increasing a runtime of the gas engine replacement device  10 . In the example illustrated, the method  430  includes connecting, using the first switch  350 , the battery pack  50  to the power switching network  310  (at block  434 ). The electronic processor  302  controls the first switch  350  to allow current flow from the battery pack  50  to the power switching network  310 . Prior to enabling the first switch  350 , the electronic processor  302  may determine whether the battery pack  50  is received in the battery receptacle  54  and whether the state of charge of the battery pack  50  is above a predetermined threshold. 
     The method  430  includes determining whether the state of charge of the battery pack  50  is below the predetermined threshold (at block  438 ). In some embodiments, the gas engine replacement device  10  includes a voltage sensor (e.g., the voltage sensor  320 ) to measure a voltage of the battery pack  50 . The electronic processor  302  determines the state of charge of the battery pack  50  using the voltage sensor. In other embodiments, the battery pack  50  includes an internal voltage sensor that determines a state of charge of the battery pack  50 . The electronic processor  302  communicates with a battery electronic processor of the battery pack  50  to receive the state of charge of the battery pack  50  from the battery electronic processor. For example, the battery pack  50  provides the state of charge information to the electronic processor  302  during a group read. 
     When the state of charge of the battery pack  50  is above the predetermined threshold, the method  430  returns to block  434  and continues to operate the gas engine replacement device  10  using the battery pack  50 . When the state of charge of the battery pack  50  is below the predetermined threshold, the method  400  includes connecting, using the second switch  354 , the module port  162  to the power switching network  310  (at block  442 ). The electronic processor  302  controls the second switch  354  to allow current flow from the module port  162  to the power switching network  310 . In other words, a battery module  158 , having an attached battery pack  50 , is coupled to the module port  162 , and when the module port  162  is connected to the power switching network  310  via the second switch  354 , power from the battery pack  50  of the battery module  158  is connected to the power switching network  310  and powers the gas engine replacement device  10 . Similarly as above, prior to enabling the second switch  354 , the electronic processor  302  may determine whether a battery module  158  including a battery pack  50  is connected to the module port  162  and whether the state of charge of the battery pack  50  received in the battery module  158  is above the predetermined threshold. 
     The method  430  also includes disconnecting, using the first switch  350 , the battery pack  50  from the power switching network  310  (at block  446 ). The electronic processor  302  controls the first switch  350  to block current flow from the battery pack  50  to the power switching network  310 . In the example illustrated in  FIG. 16 , connecting the module port  162  is performed before disconnecting the battery pack  50 . However, these steps may also be performed in the reverse order. That is, the electronic processor  302  may disconnect the battery pack  50  from the power switching network  310  before connecting the module port  162  to the power switching network  310 . Further, in some embodiments, the electronic processor  302  may disconnect the battery pack  50  from the power switching network  310  simultaneously with connecting the module port  162  to the power switching network  310 . 
     The method  430  thereby allows a user to continuously run the gas engine replacement device  10  while daisy-chaining additional battery packs  50  during operation without removing the currently mounted battery pack  50 . Such an application is useful in, for example, a stationary application, for example, pumps, concrete/mortar mixers, and the like with the battery modules  158  mounted to the power equipment. The method  430  also provides the advantage of maximum flexibility for implementing more batteries. Particularly, a user may decide how many batteries would be needed for a task. Additionally, with this embodiment, additional battery receptacles  54  are not required on the housing  14  of the gas engine replacement device  10  thereby providing a better form factor for the gas engine replacement device  10 . 
       FIG. 16  is described with respect to embodiments in which, generally, the battery pack  50  or the module port  162  is connected to the power switching network  310  at a given time during operation of the gas engine replacement device  10 , but not both packs. In other embodiments, both the battery pack  50  and the module port  162  are connected to the power switching network. For example, the battery pack  50  and the module port  162  may be connected in parallel or in series, similar to the alternative embodiments describe above with respect to  FIG. 13 . 
     In some embodiments, the motor  36  may be temporarily stopped or the operation of the motor  36  may be temporarily restricted when the electronic processor  302  is switching between power sources. For example, the electronic processor  302  may control the power switching network  310  to stop the motor  36  after determining that the first battery pack  50 A or the battery pack  50  is depleted. The electronic processor  302  then enables the first switch  350  and disables the second switch  354  before resuming the operation of the motor  36 . In some embodiments, rather than stopping the motor  36 , the electronic processor  302  may coast the motor  36  while switching between the power sources. 
       FIGS. 17A-17B  illustrate two daisy-chain circuits  450 A and  450 B, respectively, that enable daisy-chained battery packs  50  connected to the module port  162  of  FIGS. 14  and  15  to power the power switching network  310 , and, thereby, the gas engine replacement device  10 . In  FIG. 17A , the module port  162  is coupled to two module housings  164  (individually identified as  164 A and  164 B, respectively) having respective battery packs  50 . As illustrated, the cords  178 A and  178 B form a DC bus link to the module port  162 , whereby the battery pack  50  of the module housing  164 A is coupled to the bus link via a third switch  452  and the battery pack  50  of the module port  164 B is coupled to the bus link  178  via a fourth switch  454 . The third switch  452  and fourth switch  454  are selectively controlled by the electronic processor  302 . Accordingly, the respective battery packs  50  of the module housing  164 A and module housing  164 B may be selectively coupled to the module port  162  and, thus, the power switching network  310 . Returning to block  442  of  FIG. 16 , when the module port  162  is connected to the power switching network  310  via the second switch  354 , the electronic processor  302  may further provide control signals to the third switch  452 , the fourth switch  454 , or both, to select one or both of the batteries  50  coupled to the module housings  164 A-B to provide power to the power switching network  310 . The control signals may be provided from the electronic processor  302  via the module port over data lines of the cords  178 A-B. For example, a control line per module housing  164  may be provided, or a shared control line may be used with control signals having an associated address that identifies the module housing  164  to receive the control signals. The module housings  164  (or their respective switches), in turn, may act in response to control signals intended for themselves, and filter out control signals intended for other module housings  164 . 
     In  FIG. 17B , the module port  162  is again coupled to the two module housings  164  (individually identified as  164 A and  164 B, respectively) having respective battery packs  50 . As illustrated, the cords  178 A and  178 B form a DC bus link to the module port  162 , whereby the battery pack  50  of the module housings  164 A and  165 B are coupled to the bus link. Instead of individual switches included within the module housings  164 A-B, a multi-pole switch  456  is included as part of the module port  162  in the gas engine replacement device  10 . In some embodiments, the multi-pole switch  456  may be incorporated within one of the module housings  164 . The DC bus link includes separate power supply lines connecting the module port  162  to module housings  164 , one for each module housing  164 . The multi-pole switch  456  is selectively controlled by the electronic processor  302  to select one of the power supply lines of the DC bus link. Accordingly, the respective battery packs  50  of the module housing  164 A and module housing  164 B may be selectively coupled to the module port  162  and, thus, the power switching network  310 . Returning to block  442  of FIG.  16 , when the module port  162  is connected to the power switching network  310  via the second switch  354 , the electronic processor  302  may further provide control signals to the multi-pole switch  456 , to select one or both of the batteries  50  coupled to the module housings  164 A-B to provide power to the power switching network  310 . 
     While three power supply lines and a  3 -to- 1  multi-pole switch are illustrated as part of the cords  178 A and  178 B in  FIG. 17B , in some embodiments, fewer or more power supply lines are included and a multi-pole switch  456  having a corresponding number of inputs is provided. Generally, for each power supply line included, a one additional module housing  164  with battery pack  50  may be coupled in a daisy chain manner to the module port  162 . 
     With respect to the embodiments of  FIGS. 17A and 17B , the electronic controller  302  may select the battery  50  from the plurality of daisy-chained batteries  50  based on a state of charge of the batteries  50 . The battery packs  50  may include a voltage sensor or other sensor to measure their own respective state of charge, and provide the measured state of charge to the electronic controller  302  via a data line of the cords  178 A and  178 B, or the gas engine replacement device  10  may include a voltage sensor or other sensor to measure the state of charge of whichever battery pack  50  is coupled via the module port  162 . In some embodiments, when the module port  162  is selected to provide power (e.g., in step  442  of  FIG. 16 ), the electronic controller  302  determines the state of charge for each battery pack  50  connected via daisy chain to the module port  162 , and then selects the battery pack  50  having the highest state of charge. Thereafter, the electronic contro 11 er 302  may monitor the state of charge of the selected battery pack  50 , and, when the state of charge drops below a predetermined threshold, switch to the battery pack  50  having the highest state of charge at that point in time. In some embodiments, other battery pack  50  selection criteria and techniques are used to select from the battery packs  50  coupled to the module port  162 . 
     In some embodiments, as shown in  FIGS. 18-19 , the gas engine replacement device  10  includes an on-board charging circuit  460  to charge a battery pack  50  connected to the gas engine replacement device  10 . The gas engine replacement device  10  includes a power cord  464  that can be plugged into a power outlet (e.g., a 120 VAC/60 Hz wall outlet or other standard power outlet) to receive charging power to charge the battery pack  50 . The on-board charging circuit  460  receives the charging power from the power cord  464  and, when enabled, provides charging current to charge the battery pack  50 . 
       FIG. 19  is a simplified block diagram of the power source  308  according to another example embodiment. The power source  308  includes a battery pack  50  and the on-board charging circuit  460  to charge the battery pack  50 . The battery pack  50  is coupled to the power switching network  310  through a discharge switch  468 . The on-board charging circuit  460  is coupled to the battery pack  50  through a charge switch  472 . The discharge switch  468  and the charge switch  472  are, for example, FETs that are controlled by the electronic processor  302  to be enabled and disabled. When the discharge switch  468  is enabled, the discharge switch  468  allows current flow from the battery pack  50  to the power switching network  310 . When the discharge switch  468  is disabled, the discharge switch  468  blocks current flow from the battery pack  50  to the power switching network  310 . When the charge switch  472  is enabled, the charge switch  472  allows current flow from the on-board charging circuit  460  to the battery pack  50  to charge the battery pack  50 . When the charge switch  472  is disabled, the charge switch  472  blocks current flow from the on-board charging circuit  460  to the battery pack  50 . 
     In some embodiments, the electronic processor  302  may control the discharge switch  468  and the charge switch  472  such that both the discharge switch  468  and the charge switch  472  are not enabled at the same time. Accordingly, the motor  36  of the gas engine replacement device  10  may not be operating while the battery pack  50  is being charged. 
     In some embodiments, the electronic processor  302  may control the discharge switch  468  and the charge switch  472  such that both the discharge switch  468  and the charge switch  472  are enabled at the same time. Accordingly, the motor  36  of the gas engine replacement device  10  may be operating while the battery pack  50  is being charged. For example, the charging circuit  460  pay provide a trickle charge to the battery pack  50  when the power cord  464  is coupled to an AC source. Further, an AC/DC rectifier circuit may be provided in the gas engine replacement device  10  (e.g., in the on-board charging circuit  460 ) that provides DC output on a DC bus connecting the power switching network  310  and the battery pack  50 . Thus, the power switching network  310  would pull DC power from the rectifier, and the AC power from the power cord  464  would power the motor  36 . Further, when the current drawn from the rectifier is below a certain current limit for the wall outlet coupled to the power cord  464 , the excess current (the amount of current between the present current draw and the current limit) charges the battery pack  50 . In some embodiments, the DC bus includes a capacitor between the positive DC bus line and negative DC bus line, which smooths ripple on the DC bus, and the charging current is drawn from the capacitor. 
     In some embodiments, the gas engine replacement device  10  includes charge enable switch that may be actuated by a user. When the charge enable switch is actuated, the electronic processor  302  begins charging the battery pack  50  by disabling the discharge switch  468  and enabling the charge switch  472 . In some embodiments, when the electronic processor  302  determines that the state of charge of the battery pack  50  drops below a predetermined threshold (e.g., using the voltage sensor  320  or upon receiving an indication from the battery pack  50 , as described above), the electronic processor actuates the charge enable switch and deactivates the discharge switch  468 , and the on-board charging circuit  460  begins charging the battery pack  50 . 
     In one example, the gas engine replacement device  10  of  FIGS. 18-19  is used for rental fleets. Equipment rental companies may prefer to lock certain features of rented equipment to prevent theft. In the case of gas engine replacement devices  10 , the rental companies may want to lock the battery packs  50  to the gas engine replacement device  10  such that the battery packs  50  cannot be removed from the gas engine replacement device  10 . In these situations, the on-board charging circuit  460  may be used to charge the battery pack  50  while the battery pack  50  is coupled to the gas engine replacement device  10 . 
       FIG. 1-18  are shown as including separate embodiments of the gas engine replacement device  10 . However, it should be understood that the features of any of these embodiments may be combined with features of other embodiments. For example, the gas engine replacement device  10  may include multiple battery receptacles  54  as well as the module port  162  to connect to one or more battery modules  158 . Additionally, the gas engine replacement device  10  may include an on-board charging circuit  460  as well as multiple battery receptacles  54  and/or the module port  162 . Further, it should be understood that the one or more battery receptacles  54  may receive a battery pack  50  of any configuration. For example, the first battery receptacle  54 A may receive the battery pack  50 - 1  having a first configuration and the second battery receptacle  54 B may receive the battery pack  50 - 2  having a second configuration. Additionally, a user may replace the battery pack  50 - 1  having a first configuration and received in the battery receptacle  54  with the battery pack  50 - 2  having a second configuration. Thus, in some of the embodiments of the gas engine replacement devices  10  described above, the gas engine replacement device  10  is configured to be coupled to different types of the battery pack  50 .