Patent Publication Number: US-2023147651-A1

Title: Multi-battery management for a portable device

Description:
TECHNICAL FIELD 
     The present invention relates generally to batteries and, more particularly, to battery management for portable devices. 
     BACKGROUND OF THE INVENTION 
     The use of various forms of batteries has become nearly ubiquitous in today&#39;s world. As more and more portable or cordless devices, such as power tools (e.g., drills, saws, grass trimmers, blowers, sanders, etc.), small appliances (e.g., mixers, blenders, coffee grinders, etc.), communications devices (e.g., smartphones, personal digital assistants, etc.), and office equipment (e.g., computers, tablets, printers, etc.), are in widespread use, the use of battery technologies of varying chemistry and configuration is commonplace. 
     A cordless device may power components using a single battery or multiple batteries. For some applications, use of multiple batteries can provide better performance as compared to use of a single battery, such as by enabling a greater range of current that can be supplied to components of a portable device. Further, use of multiple batteries can increase reliability of a portable device. 
     In some circumstances, implementation of multiple batteries in a portable device is expensive. For example, a “matching” process may be performed during device fabrication or assembly to ensure that the batteries have similar characteristics, such as charge capacity, charge rate, discharge rate, impedance, or other characteristics. In some cases, one or more batteries may be unused, replaced, and/or discarded due to being “mismatched” to other batteries. As a result, product yield can be reduced, increasing cost associated with a portable device. Further, if one or more characteristics of batteries of a portable device are mismatched, performance may be degraded. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an aspect of the disclosure, a portable device includes a multi-battery management device configured to perform battery management operations, such as a battery “balancing” process. The multi-battery management device may selectively connect or disconnect batteries of the portable device from one or more components of the portable device, such as an electric motor of the portable device. The multi-battery management device may be configured to perform the connection or disconnection based on a difference between voltage levels of the batteries, based on a magnitude of a current supplied to the one or more components, or a combination thereof. 
     To illustrate, in one example, the multi-battery management device may compare the difference between the voltage levels of the batteries to a first threshold. In response to the difference satisfying (e.g., being greater than, or being greater than or equal to) the first threshold, the multi-battery management device may disconnect one of the batteries from the one or more components. The multi-battery management device may be configured to select the battery with the lower voltage level for disconnection (e.g., to avoid charging of the battery by another battery) and may provide power to the one or more components using the battery with the greater voltage level. Alternatively, if the difference between the voltage levels of the batteries fails to satisfy the first threshold, then both the batteries may be connected to the one or more components. 
     In an illustrative example, the multi-battery management device is configured to determine a magnitude of a current provided to the one or more components. In response to the magnitude of the current satisfying a second threshold, the multi-battery management device may couple each of the batteries to the one or more components (e.g., irrespective of the voltage levels of the batteries). As a result, power provided to the one or more components may be increased (e.g., during a high-power activity, such as where a motor produces a large amount of horsepower or torque). 
     Selectively connecting and disconnecting batteries using the multi-battery management device may improve performance, reliability, or lifespan of a portable device. For example, by selectively disconnecting a battery, repetitive charging and discharging of one battery by another battery may be reduced or avoided. As a result, battery lifespan may be extended for some battery technologies. 
     Further, in some cases, use of the multi-battery management device may enable a more “relaxed” matching process during device fabrication or assembly. For example, by compensating for differences between batteries (e.g., charge capacity, charge rate, discharge rate, or impedance) using selective connection and disconnection of batteries, a tolerance range for matching batteries may be relaxed, increasing product yield. Alternatively or in addition, one or more testing operations of the matching process may be omitted, such as by omitting testing of charge capacity, charge rate, discharge rate, impedance, one or more other characteristics, or a combination thereof. 
     In addition, use of switchable parallel-connected batteries in accordance with some aspects of the disclosure may avoid certain drawbacks associated with series-connected batteries. To illustrate, certain conventional portable devices avoid battery-to-battery charging by implementing a power source that includes multiple batteries connected in series. As a result, output power is increased (due to increased voltage of the power source), which may involve redesigning one or more device components to accommodate the increased voltage (e.g., by implementing a higher-power motor and control circuit that are compatible with the increased voltage). By using switchable parallel-connected batteries in accordance with some aspects of the disclosure, output power can be increased without a redesign to implement higher-power components (thus reducing device cost) and while reducing or avoiding battery-to-battery charging as in some conventional multi-battery designs. 
     Further, use of multiple switchable batteries in accordance with some aspects of the disclosure may increase an amount of power available to one or more device components (e.g., an electric motor) while also providing certain advantages associated with single-battery implementations. For example, in some portable devices, a battery having a low voltage state may cause a power-down or shut-off event of the portable device. In a portable device according to some aspects of the disclosure, a first battery having a low voltage can be disconnected from one or more components prior to the low voltage causing a power-off state of the portable device. The portable device may continue to operate using a second battery having a greater voltage than the first battery. In this state, the portable device may operate using a low-power or reduced-power mode, which may be preferable in some cases to entering a shut-off state as in certain conventional portable devices. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG.  1    shows an example of a portable device that includes a battery management device in accordance with some aspects of the disclosure; 
         FIG.  2    shows a flow chart illustrating an example of a method of operation of a portable device, such as the portable device of  FIG.  1   , in accordance with some aspects of the disclosure; 
         FIG.  3    shows an example of an electric mower configuration of the portable device of  FIG.  1    in accordance with some aspects of the disclosure; 
         FIG.  4    shows an example of an electric blower configuration of the portable device of  FIG.  1    in accordance with some aspects of the disclosure; 
         FIG.  5    shows examples of circuits that may be included in a portable device, such as the portable device of  FIG.  1   , in accordance with some aspects of the disclosure; 
         FIGS.  6 A,  6 B,  6 C,  6 D,  6 E,  6 F,  6 G,  6 H, and  6 I  show additional examples of circuits that may be included in a portable device, such as the portable device of  FIG.  1   , in accordance with some aspects of the disclosure; and 
         FIGS.  7 A and  7 B  show examples of devices that may be included in a portable device, such as the portable device of  FIG.  1   , in accordance with some aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG.  1   , a particular illustrative example of a portable device is depicted and generally designated  100 . The portable device  100  may correspond to a cordless power tool, such as an electric mower, an electric blower, or another power tool, as illustrative examples. In another example, the portable device  100  may correspond to another device, such as a cordless home appliance. In an additional example, the portable device  100  may correspond to a personal electronic device, such as a phone or a computer. 
     The portable device  100  includes one or more components  102  and a multi-battery power source  130 . The one or more components  102  are configured to receive power from the multi-battery power source  130 . In some examples, the one or more components  102  include an electric motor  104  of the portable device  100 . 
     The multi-battery power source  130  includes a plurality of batteries. In the example of  FIG.  1   , the multi-battery power source  130  includes a first battery  132  and a second battery  134 . In some examples, the second battery  134  is coupled in parallel to the first battery  132  or is configured to discharge in parallel with the first battery  132 . Although two batteries  130 ,  132  are illustrated in the example of  FIG.  1   , in other examples, the multi-battery power source  130  may include a different number of batteries, such as three batteries, four batteries, or five batteries, etc. The multi-battery power source  130  is configured to provide a current C 1  to the one or more components  102 . 
     The current C 1  is generated at least in part using the first battery  132  and the second battery  134 . In one example, a first current provided by the first battery  132  is summed with a second current provided by the second battery  134  to generate the current C 1 . 
     In some examples, the multi-battery power source  130  includes one or more battery packs. A battery pack may include one or more batteries integrated within a battery enclosure, such as a protective battery casing. A battery enclosure may include a plastic material or a wrap material molded about the one or more batteries, as illustrative examples. To further illustrate, in one example, the first battery  132  includes a first battery pack, and the second battery  134  includes a second battery pack that is distinct from the first battery pack. In other examples, the first battery  132  and the second battery  134  are integrated within a common battery pack (or other device). In some examples, the first battery  132  and the second battery  134  include lithium-ion (Li-ion) batteries or one or more Li-ion battery packs. In other implementations, one or more other battery types may be used. 
     The portable device  100  further includes a multi-battery management device  110 . The multi-battery management device  110  is coupled to the multi-battery power source  130 . In the example of  FIG.  1   , the multi-battery management device  110  includes a sensor interface  112 , a comparison circuit  114 , and a control circuit  122 . 
     The control circuit  122  may include a plurality of switch devices, such as a first switch device  124  and a second switch device  126 . Each switch device  124 ,  126  may include one or more transistors. In one example, each switch device  124 ,  126  includes a plurality of field-effect transistors (FETs). The first switch device  124  is coupled to the first battery  132 , and the second switch device  126  is coupled to the second battery  134 . The first battery  132  is coupled to the one or more components  102  via the first switch device  124 , and the second battery  134  is coupled to the one or more components  102  via the second switch device  126 . 
     The portable device  100  may further include one or more battery sensors  136 . The one or more battery sensors  136  may be coupled to the multi-battery power source  130  (e.g., to the first battery  132  and to the second battery  134 ). The one or more battery sensors  136  may be further coupled to the multi-battery management device  110  (e.g., to the sensor interface  112 ). 
     The portable device  100  may further include a power-up switch  106 . The power-up switch  106  may be coupled to the one or more components  102  and to the multi-battery management device  110  (e.g., to the sensor interface  112 ). 
     During operation, the multi-battery power source  130  may supply power to the one or more components  102 . To illustrate, in one example, the portable device corresponds to an electric mower, and the multi-battery power source  130  is configured to supply power to the electric motor  104  to operate a blade of the electric mower. In another example, the portable device corresponds to an electric blower, and the multi-battery power source  130  is configured to supply power to the electric motor  104  to operate a fan of the electric blower. 
     Batteries of the multi-battery power source  130  may be recharged using a power source. In some examples, the portable device  100  is configured to recharge batteries of the multi-battery power source  130  using a mains electricity supply. For example, the portable device  100  may include a power supply port that is configured to couple to a mains electricity outlet via a power supply device. Alternatively or in addition, batteries of the multi-battery power source  130  may be recharged using another energy recovery mechanism. To illustrate, batteries of the multi-battery power source  130  may be recharged using a regenerative energy recovery mechanism that slows a component (e.g., a rotor or other moving component) of the electric motor  104  by converting kinetic energy of the component to voltage that is supplied to the multi-battery power source  130  to recharge one or both of the first battery  132  and the second battery  134 . 
     In some cases, batteries of the multi-battery power source  130  may discharge at different rates, may charge at different rates, or both. For example, trace differences in impedances associated with the first battery  132  and the second battery  134  (or other components connected to the first battery  132  and the second battery  134 ) may cause the first battery  132  and the second battery  134  to discharge unequally, to charge unequally, or both. As another example, a temperature difference between the first battery  132  and the second battery  134  (or other components) may cause the first battery  132  and the second battery  134  to discharge unequally, to charge unequally, or both. Further, in some cases, charge capacity or other characteristics of the first battery  132  may differ with respect to the second battery  134 . As a result, a first voltage level V 1  of the first battery  132  may differ from a second voltage level V 2  of the second battery  134  in some cases. 
     In accordance with an aspect of the disclosure, the multi-battery management device  110  is configured designate, based on voltage levels of batteries of the multi-battery power source  130 , at least one battery of the multi-battery power source  130  as a primary battery and to disconnect one or more other batteries of the multi-battery power source  130  from the one or more components  102 . By disconnecting one or more batteries from the one or more components  102 , the multi-battery management device  110  may reduce or avoid exchange of energy between batteries (e.g., where one battery provides energy to another battery instead of providing the energy to the one or more components  102 ). As a result, power supplied to the one or more components  102  may be increased as compared to systems in which at least some power is transferred from one battery to another battery during discharging (instead of to the one or more components  102 ), improving performance and user experience associated with the portable device  100 . 
     To enable battery management operations, the multi-battery management device  110  is configured to receive one or more signals indicating operational characteristics of the first battery  132  and the second battery  134 . To illustrate, the one or more signals may include a first indication  138  of the first voltage level V 1  of the first battery  132 , a second indication  140  of the second voltage level V 2  of the second battery  134 , and a third indication  142  of a magnitude of the current C 1 . In one example, the sensor interface  112  is configured to initiate a sensor operation performed by the one or more battery sensors  136  to generate the first indication  138  of the first voltage level V 1  of the first battery  132 , the second indication  140  of the second voltage level V 2  of the second battery  134 , and the third indication  142  of the magnitude of the current C 1 . The sensor interface  112  may be configured to receive the first indication  138  of the first voltage level V 1 , the second indication  140  of the second voltage level V 2 , and the third indication of the magnitude of the current C 1  from the one or more battery sensors  136 . 
     In some implementations, the sensor interface  112  is configured to perform one or more operations based on the first indication  138 , the second indication  140 , and the third indication  142 . For example, depending on the particular implementation, the sensor interface  112  may be configured to perform a digital-to-analog (DAC) conversion operation or an analog-to-digital (ADC) conversion operation based on the first indication  138 , the second indication  140 , and the third indication  142 . In another example, the sensor interface  112  may include one or more drivers configured to convert the first indication  138 , the second indication  140 , and the third indication  142  from a first supply voltage associated with a first voltage domain of the one or more battery sensors  136  to a second supply voltage associated with a second voltage domain of the multi-battery management device  110 . Alternatively or in addition, the sensor interface  112  may be configured to perform impedance adjustment to match an input impedance of the multi-battery management device  110  to an output impedance of the one or more battery sensors  136 . 
     The comparison circuit  114  is configured to receive, from the sensor interface  112 , the first indication  138 , the second indication  140 , and the third indication  142  (or signals corresponding to the first indication  138 , the second indication  140 , and the third indication  142 ). The comparison circuit  114  is configured to determine a difference between the first voltage level V 1  and the second voltage level V 2 . For example, the comparison circuit  114  may be configured to determine the difference by subtracting the first voltage level V 1  from the second voltage level V 2  (or vice versa). 
     The comparison circuit  114  is configured to compare the difference to a first threshold  116 . The comparison circuit  114  may be configured to generate a first output indicating whether the difference satisfies (e.g., is greater than, or is greater than or equal to) the first threshold  116 . 
     The control circuit  122  is configured to disconnect one of the first battery  132  or the second battery  134  from the one or more components  102  based at least in part on the difference between the first voltage level V 1  and the second voltage level V 2  satisfying the first threshold  116 . For example, if the difference indicates that the first voltage level V 1  is significantly larger than the second voltage level V 2 , then the second switch device  126  may be deactivated to decouple the second battery  134  from the one or more components  102  (and to reduce or avoid charging of the second battery  134  by the first battery  132 ). As another example, if the difference indicates that the second voltage level V 2  is significantly larger than the first voltage level V 1 , then the first switch device  124  may be deactivated to decouple the first battery  132  from the one or more components  102  (and to reduce or avoid charging of the first battery  132  by the second battery  134 ). 
     In one example, the comparison circuit  114  is configured to provide one or more control signals to the control circuit  122  to selectively activate (or deactivate) the switch devices  124 ,  126 . For example, the comparison circuit  114  may be configured to provide a control signal  120  (e.g., a multi-bit control signal) to the first switch device  124  or to the second switch device  126 . In one example, the control signal  120  has a particular value that activates (or deactivates) the first switch device  124  or the second switch device  126 . As an illustrative example, a first value (e.g., a logic zero value) of the control signal  120  may activate the first switch device  124  to couple the first battery  132  to the one or more components  102 , and a second value (e.g., a logic one value) may deactivate the first switch device  124  to disconnect the first battery  132  from the one or more components  102 . Further, similar control mechanisms may be provided for the second battery  134  (e.g., by providing a second control signal to the second switch device  126  similarly to the control signal  120  and the first switch device  124 ). 
     The multi-battery management device  110  is configured to select the first battery  132  for disconnection or the second battery  134  for disconnection based on a comparison of the voltage levels V 1  and V 2 . For example, the multi-battery management device  110  may select the first battery  132  for disconnection based on the first voltage level V 1  being less than the second voltage level V 2 . In another example, the multi-battery management device  110  may select the second battery  134  for disconnection based on the second voltage level V 2  being less than the first voltage level V 1 . 
     In some implementations, a battery management operation is performed further based on the magnitude of the current C 1 . For example, if the magnitude of the current C 1  is relatively large, then both batteries  132 ,  134  may be connected to the one or more components  102  (e.g., irrespectively of whether the difference between the first voltage level V 1  and the second voltage level V 2  satisfies the first threshold  116 ). In this case, both batteries  132 ,  134  may be used to enable a high-power mode of operation of the portable device  100 . In another example, if the magnitude of the current C 1  is relatively small, then one or both batteries  132 ,  134  may be selectively connected to the one or more components  102  (e.g., based on whether the difference between the first voltage level V 1  and the second voltage level V 2  satisfies the first threshold  116 ). 
     To further illustrate, the comparison circuit  114  may be configured to compare the magnitude of the current C 1  to a second threshold  118 . The comparison circuit  114  may be configured to generate a second output indicating whether the magnitude of the current C 1  satisfies (e.g., is greater than, or is greater than or equal to) the second threshold  118 . The comparison circuit  114  may be configured to set a value of the control signal  120  based on whether the difference between the first voltage level V 1  and the second voltage level V 2  satisfies the first threshold  116 , based on whether the magnitude of the current C 1  satisfies the second threshold  118 , or both. 
     For example, the control signal  120  may have a first value (e.g., a logic zero value) if the difference between the first voltage level V 1  and the second voltage level V 2  fails to satisfy the first threshold  116 , if the magnitude of the current C 1  satisfies the second threshold  118 , or both. In this example, both the batteries  132 ,  134  may supply power to the one or more components  102 . 
     The control signal  120  may have a second value (e.g., a logic one value) if the difference between the first voltage level V 1  and the second voltage level V 2  satisfies the first threshold  116  and if the magnitude of the current C 1  fails to satisfy the second threshold  118 . In this case, a battery having a lower voltage level may be disconnected from the one or more components  102  via the control signal  120 . For example, the second value of the control signal  120  may be provided to the first switch device  124  to disconnect the first battery  132  from the one or components  102  if the difference between the first voltage level V 1  and the second voltage level V 2  satisfies the first threshold  116 , if the magnitude of the current C 1  fails to satisfy the second threshold  118 , and if the first voltage level V 1  is less than the second voltage level V 2 . In another example, the second value of the control signal  120  may be provided to the second switch device  126  to disconnect the second battery  134  from the one or components  102  if the difference between the first voltage level V 1  and the second voltage level V 2  satisfies the first threshold  116 , if the magnitude of the current C 1  fails to satisfy the second threshold  118 , and if the second voltage level V 2  is less than the first voltage level V 1 . 
     After disconnecting one of the first battery  132  or the second battery  134  from the one or more components  102 , power may be provided to the one or more components  102  from the other of the first battery  132  or the second battery  134 . Alternatively, when both the first battery  132  and the second battery  134  are coupled to the one or more components  102 , then power is provided to the one or more components  102  from both the first battery  132  and the second battery  134 . 
     In some implementations, the multi-battery management device  110  is configured to detect a battery management trigger event and to initiate a battery management operation based on the battery management trigger event. In some examples, detecting the battery management trigger event includes detecting a power-up event at the portable device  100  (e.g., in response to user input received via the power-up switch  106 ), such as by detecting a power-up signal generated by the power-up switch  106  in response to user input received via the power-up switch  106 . The power-up switch may be provided to the electric motor  104  to begin operation of the electric motor  104 . For example, the multi-battery power source  130  may provide the current C 1  to the one or more components  102  in response to the power-up event. 
     In response to detecting the battery management trigger event, the multi-battery management device  110  may determine the first voltage level V 1  of the first battery  132  and the second voltage level V 2  of the second battery  134 . In one example, the sensor interface  112  is configured to initiate a sensor operation performed by the one or more battery sensors  136  in response to the battery management trigger event. For example, in response to receiving a power-up signal from the power-up switch  106 , the sensor interface  112  may provide an enable signal to the one or more battery sensors  136  to initiate the sensor operation. 
     Alternatively or in addition, a battery management trigger event may include or correspond to one or more other events. For example, a battery management operation may be performed periodically or pseudo-periodically at the portable device  100 . To illustrate, the portable device  100  may include a counter configured to store a value indicating an amount of time (e.g., a number of clock cycles) since a previous battery management operation. In response to detecting that the value satisfies a threshold, the multi-battery management device  110  may trigger a battery management operation (e.g., by triggering the one or more battery sensors  136  to measure or re-measure the first voltage level V 1 , the second voltage level V 2 , and the magnitude of the current C 1 ) and may reset the value of the counter. 
     Alternatively or in addition, a battery management operation may be performed in response to detecting connection of the portable device  100  to a power source, in response to detecting disconnection of the portable device  100  from a power source, or both. To illustrate, a battery management operation may be performed in response to detecting that the portable device  100  is connected to a mains electricity outlet, in response to detecting that the portable device  100  is disconnected from a mains electricity outlet, or both. 
     In some examples, after changing operation to a single-battery mode of operation or a multi-battery mode of operation, the multi-battery management device  110  is configured to monitor indications of the voltage levels V 1 , V 2  and the magnitude of the current C 1  to determine whether to revert to the multi-battery mode or the single-battery mode. For example, the multi-battery management device  110  may be configured to revert from the single-battery mode to the multi-battery mode in response to detecting that the difference between the voltage levels V 1 , V 2  no longer satisfies the first threshold  116  (or a third threshold) or that the magnitude of the current C 1  satisfies the second threshold  118  (or a fourth threshold). 
     One or more aspects described with reference to  FIG.  1    may improve performance of a portable device  100 . For example, selectively connecting and disconnecting the batteries  132 ,  134  using the multi-battery management device  110  may improve performance, reliability, or lifespan of the multi-battery power source  130 . As a particular example, by selectively disconnecting a battery of the multi-battery power source  130 , repetitive charging and discharging of the battery by another battery of the multi-battery power source  130  may be reduced or avoided. As a result, battery lifespan may be extended for some battery technologies. 
     Further, in some cases, use of the multi-battery management device  110  may enable a more “relaxed” matching process during fabrication or assembly of the portable device  100 . For example, by compensating for differences between the batteries  132 ,  134  (e.g., charge capacity, charge rate, discharge rate, or impedance) using selective connection and disconnection of the batteries  132 ,  134 , a tolerance range for matching batteries may be relaxed. Alternatively or in addition, one or more testing operations of the matching process may be omitted, such as by omitting testing of the batteries  132 ,  134  for charge capacity, charge rate, discharge rate, impedance, one or more other characteristics, or a combination thereof. 
     Although certain examples are described with reference to connecting a single battery of the multi-battery power source  130  to the one or more components  102  and disconnecting a single battery of the multi-battery power source  130  from the one or more components  102 , it is noted that other examples are also within the scope of the disclosure. For example, multiple batteries of the multi-battery power source  130  can be connected to the one or more components  102  while another battery of the multi-battery power source  130  is disconnected from the one or more components  102 . Alternatively or in addition, one battery of the multi-battery power source  130  can be connected to the one or more components  102  while multiple other batteries of the multi-battery power source  130  are disconnected from the one or more components  102 . Alternatively or in addition, multiple batteries of the multi-battery power source  130  can be connected to the one or more components  102  while multiple other batteries of the multi-battery power source  130  are disconnected from the one or more components  102 . 
     It is noted that the features described with reference to the multi-battery management device  110  can be implemented using a variety of components or techniques, such as digital circuits, analog circuits, mixed-signal circuits, or a combination thereof. To illustrate, in some examples, the comparison circuit  114  includes analog hardware, such as one or more operational amplifiers (op amps) configured to perform comparisons of signals and to generate outputs indicating results of the comparisons. Alternatively or in addition, the multi-battery management device  110  may include a memory and a processor configured to retrieve instructions from the memory. The processor may execute the instructions to perform operations described herein. For example, the processor may execute a compare instruction to perform operations described with reference to the comparison circuit  114 . Further, although two batteries  132 ,  134  are described for illustration, in other examples, one or more multi-battery management operations described herein can be applied to a different number of batteries, such as three or more batteries. 
     Referring to  FIG.  2   , a particular illustrative example of a method is depicted and generally designated  200 . In some examples, operations of the method  200  are performed by a portable device, such as the portable device  100  of  FIG.  1   . 
     The method  200  includes initiating a power-up operation by a handle switch, at  202 . For example, the power-up switch  106  may correspond to a handle switch of the portable device  100 . The power-up operation may be initiated in response to activation of the power-up switch  106 . 
     The method  200  further includes determining whether a difference between voltage levels of batteries satisfies a threshold, at  204 . For example, the multi-battery management device  110  may determine whether either the first voltage level V 1  minus the second voltage level V 2  or the second voltage level V 2  minus the first voltage level V 1  is less than or equal to the first threshold  116 . In the non-limiting example of  FIG.  2   , the first threshold  116  may correspond to 0.7 volts (V). In other examples, the first threshold  116  may correspond to another value. 
     In response to determining that the difference satisfies the threshold (e.g., where the difference is greater than 0.7 V), the method  200  further includes operating according to a single-battery discharge mode, at  206 . For example, the first battery  132  may be coupled to the one or more components  102  by activating the first switch device  124 , and the second battery  134  may be decoupled from the one or more components  102  by deactivating the second switch device  126 . 
     The method further includes selectively activating field-effect transistors (FETs) for a higher-voltage battery and deactivating FETs for a lower-voltage battery, at  208 . For example, the first switch device  124  may be activated and the second switch device  126  may be deactivated in response to determining that the first voltage V 1  is greater than the second voltage V 2 . In another example, the second switch device  126  may be deactivated and the first switch device  124  may be activated in response to determining that the second voltage V 2  is greater than the first voltage V 1 . 
     Alternatively, in response to determining that the difference fails to satisfy the threshold (e.g., where the difference is less than or equal to 0.7 V), the method  200  includes operating according to a multi-battery discharge mode, at  210 . For example, both the first battery  132  and the second battery  134  may be coupled to the one or more components  102  via the first switch device  124  and the second switch device  126 , respectively. 
     The method  200  further includes determining whether a loading current exceeds a threshold, at  212 . For example, the multi-battery management device  110  may determine whether the magnitude of the current C 1  satisfies the second threshold  118 . In the non-limiting example of  FIG.  2   , the second threshold  118  may correspond to three to five amps (A). In other examples, the second threshold  118  may correspond to another value. 
     In response to the loading current failing to exceed the threshold, the method  200  continues, at  206 . Alternatively, in response to the loading current exceeding the threshold, the method  200  includes activating discharge FETs for both batteries, at  214 . For example, both the first switch device  124  and the second switch device  126  may be activated to couple the first battery  132  and the second battery  134  to the one or more components  102 . 
     One or more aspects described with reference to  FIG.  2    may improve performance of a portable device. For example, selectively connecting and disconnecting batteries may improve performance, reliability, or lifespan of the batteries. As a particular example, by selectively disconnecting a battery, repetitive charging and discharging of the battery by another battery may be reduced or avoided. As a result, battery lifespan may be extended for some battery technologies. 
     Further, in some cases, selectively connecting and disconnecting batteries may enable a more “relaxed” matching process during fabrication or assembly of a portable device. For example, by compensating for differences between batteries (e.g., charge capacity, charge rate, discharge rate, or impedance) using selective connection and disconnection of the batteries, a tolerance range for matching batteries may be relaxed. Alternatively or in addition, one or more testing operations of the matching process may be omitted, such as by omitting testing of the batteries for charge capacity, charge rate, discharge rate, impedance, one or more other characteristics, or a combination thereof. 
       FIG.  3    depicts one illustrative configuration of the portable device  100 . In the example of  FIG.  3   , the portable device  100  corresponds to an electric mower. In  FIG.  3   , the electric motor  104  may be configured to operate a blade of the portable device  100 . For example, the electric motor  104  may include a stator configured to receive the current C 1  and to generate an electromagnetic field based on the current C 1 . The electric motor  104  may further include a rotor configured to apply torque to a driveshaft in response to the electromagnetic field to turn the blade. 
     In some aspects of the disclosure, use of multiple switchable batteries in an electric mower reduces or avoids certain drawbacks associated with an electric mower that includes series-connected batteries. To illustrate, certain conventional electric mowers avoid battery-to-battery charging by implementing a power source that includes multiple batteries connected in series. As a result, output power is increased (due to increased voltage of the power source), which may involve redesign of one or more device components to accommodate the increased voltage (e.g., by implementing a higher-power motor and control circuit that are compatible with the increased voltage). By using switchable parallel-connected batteries in accordance with some aspects of the disclosure, output power of an electric mower can be increased without a redesign to implement higher-power components (thus reducing cost of the electric mower) while reducing or avoiding battery-to-battery charging as in some conventional multi-battery designs. 
       FIG.  4    depicts another illustrative configuration of the portable device  100 . In the example of  FIG.  4   , the portable device  100  corresponds to an electric blower (e.g., a handheld electric blower or a wearable electric blower, such as a backpack-mounted electric blower). In  FIG.  4   , the electric motor  104  may be configured to operate a fan of the portable device  100 . For example, the electric motor  104  may be configured to rotate a fan in response to the current C 1 . Rotation of the fan may draw air into the electric blower (e.g., due to a centrifugal force created by rotation of the fan), and the air may be compressed and emitted from a tube of the electric blower. 
     It is noted that various values and parameters described herein can have a value selected based on the particular application. For example, in the electric mower implementation of  FIG.  3   , higher voltage batteries may be used as compared to the electric blower implementation of  FIG.  4   . As an illustrative example, battery voltages of 58 V may be used for an electric blower implementation, and battery voltages of 18 V may be used for an electric mower implementation. Further, values of the first threshold  116  and the second threshold  118  may be selected based on the particular implementation, such as based on the battery voltages. As an example, the illustrative thresholds described with reference to  FIG.  2    may be compatible with some implementations but not other implementations. 
     In some aspects of the disclosure, use of multiple switchable batteries in an electric blower reduces or avoids certain drawbacks associated with an electric blower that includes series-connected batteries. To illustrate, certain conventional electric blowers avoid battery-to-battery charging by implementing a power source that includes multiple batteries connected in series. As a result, output power is increased (due to increased voltage of the power source), which may involve redesign of one or more device components to accommodate the increased voltage (e.g., by implementing a higher-power motor and control circuit that are compatible with the increased voltage). By using switchable parallel-connected batteries in accordance with some aspects of the disclosure, output power of an electric blower can be increased without a redesign to implement higher-power components (thus reducing cost of the electric blower) and while reducing or avoiding battery-to-battery charging as in some conventional multi-battery designs. 
       FIG.  5    illustrates examples of circuits that may be included in the portable device  100 . In some examples, the circuits of  FIG.  5    are included in or correspond to the multi-battery management device  110  of  FIG.  1   . 
     The circuits of  FIG.  5    may include a first drive circuit  510 , a second drive circuit  520 , and a microcontroller (MCU)  530 .  FIG.  5    also depicts an illustrative, non-limiting example of a comparison circuit  540  (e.g., the comparison circuit  114 ). In some examples, the first drive circuit  510 , the second drive circuit  520 , the MCU  530 , and the comparison circuit  540  are included in or correspond to the multi-battery management device  110  of  FIG.  1   . The circuits of  FIG.  5    may also include a first MCU write-into-port circuit  560 , a MCU power supply circuit  570 , and a second MCU write-into-port circuit  580 . 
     In one example, the comparison circuit  540  includes a connection W 1  to a first terminal (e.g., a positive terminal) of the first battery  132  and further includes a connection W 5  to a second terminal (e.g., a negative or ground terminal) of the first battery  132 . The comparison circuit  540  may further include a connection W 2  to a first terminal (e.g., a positive terminal) of the second battery  134  and may further include a connection W 6  to a second terminal (e.g., a negative or ground terminal) of the second battery  134 . 
     In some examples, the connections W 1 , W 2 , W 5 , and W 6  are directly coupled to the batteries  132 ,  134 . In this case, the comparison circuit  540  is directly coupled to the batteries  132 ,  134  via the connections W 1 , W 2 , W 5 , and W 6 . In some other implementations, the comparison circuit  540  may be coupled to the batteries  132 ,  134  via the sensor interface  112  and the one or more battery sensors  136  of  FIG.  1   . As an illustrative example, in some implementations, the comparison circuit  540  includes a digital circuit that receives a digitized representation of the voltage levels V 1 , V 2 , via the sensor interface  112  and the one or more battery sensors  136 . 
     The comparison circuit  540  may further include connections W 3 , W 4  that are coupled to the one or more components  102 . For example, the connections W 3 , W 4  may be coupled to input terminals of the electric motor  104 . In some examples, the connection W 3  is configured to supply the current C 1  to the one or more components  102  (e.g., to the electric motor  104 ). 
     In  FIG.  5   , the comparison circuit  540  further includes a first comparator U 2 A and a second comparator U 2 B. Further, the comparison circuit  540  may include or may be coupled to a first switch device Q 8  (e.g., the first switch device  124 ) and a second switch device Q 9  (e.g., the second switch device  126 ). In some implementations, each switch device Q 8 , Q 9  includes a metal-oxide-semiconductor field-effect transistor (MOSFET), such as an enhancement-mode n-channel MOSFET, as an illustrative example. In other examples, each switch device Q 8 , Q 9  may have a different configuration. In addition, the comparison circuit  540  may include or may be coupled to a first transient-voltage-suppression diode (TVS 1 ) and to a second TVS diode (TVS 2 ). In some examples, the switch devices Q 8 , Q 9  and the TVS diodes TVS 1 , TVS 2  correspond to or are included in the control circuit  122  of  FIG.  1   . In  FIG.  5   , the switch devices Q 8 , Q 9  and the TVS diodes TVS 1 , TVS 2  are coupled to a ground node GND. 
     In some examples, the comparison circuit  540  is coupled to the MCU  530 . For example, an output of the first comparator U 2 A may be coupled to an input (e.g., port “2”) of the MCU  530 . As another example, an output of the second comparator U 2 B may be coupled to another input (e.g., port “5”) of the MCU  530 . The first comparator U 2 A may be configured to generate an output BAT 1 _FB and to provide the output BAT 1 _FB to the MCU  530 . The second comparator U 2 B may be configured to generate an output BAT 2 _FB and to provide the output BAT 2 _FB to the MCU  530 . 
     In some implementations, the MCU  530  is coupled to the drive circuits  510 ,  520 . For example, an output (e.g., port “6”) of the MCU  530  may be coupled to an input of the first drive circuit  510 . As another example, another output (e.g., port “7”) of the MCU  530  may be coupled to an input of the second drive circuit  520 . The MCU  530  may be configured to provide a first control signal CTR_BAT_ 1  to the first drive circuit  510  and to provide a second control signal CTR_BAT_ 2  to the second drive circuit  520 . 
     The drive circuits  510 ,  520  may be coupled to the switch devices Q 8 , Q 9 . For example, the first drive circuit  510  may include an output coupled to a gate terminal of the first switch device Q 8 . The output of the first drive circuit  510  may be configured to provide a first battery enable signal BAT 1 _EN to the gate terminal of the first switch device Q 8 . As another example, the second drive circuit  520  may include an output coupled to a gate terminal of the second switch device Q 9 . The output of the second drive circuit  520  may be configured to provide a second battery enable signal BAT 2 _EN to the gate terminal of the second switch device Q 9 . 
     During operation, the comparators U 2 A, U 2 B may compare a difference between the voltage levels V 1 , V 2  to a reference voltage (e.g., the first threshold  116 ) and may compare the current C 1  to a reference current (e.g., the second threshold  118 ). The outputs BAT 1 _FB, BAT 2 _FB may indicate results of the comparisons performed by the comparators U 2 A, U 2 B. For example, the outputs BAT 1 _FB, BAT 2 _FB may indicate whether a first difference (V 1 −V 2 ) satisfies the first threshold  116 , whether a second difference (V 2 −V 1 ) satisfies the first threshold  116 , and whether the current C 1  satisfies the second threshold  118 . 
     For example, the first output BAT 1 _FB may have one of a first value or a second value. The first value may indicate that a first difference (e.g., V 1 −V 2 ) satisfies the first threshold  116  and may further indicate that the magnitude of the current C 1  fails to satisfy the second threshold  118 . The second value may indicate that the first difference (e.g., V 1 −V 2 ) fails to satisfy the first threshold  116 , that the magnitude of the current C 1  satisfies the second threshold  118 , or both. The first value may be associated with a single-battery mode that uses the first battery  132 . The second value may be associated with a multi-battery mode that uses the batteries  132 ,  134 . 
     As another example, the second output BAT 2 _FB may have one of a third value or a fourth value. The third value may indicate that a second difference (e.g., V 2 -V 1 ) satisfies the first threshold  116  and may further indicate that the magnitude of the current C 1  fails to satisfy the second threshold  118 . The fourth value may indicate that the second difference (e.g., V 2 −V 1 ) fails to satisfy the first threshold  116 , that the magnitude of the current C 1  satisfies the second threshold  118 , or both. The third value may be associated with a single-battery mode that uses the second battery  134 . The fourth value may be associated with a multi-battery mode that uses the batteries  132 ,  134 . 
     In response to the outputs BAT 1 _FB, BAT 2 _FB, the MCU  530  may select an operating mode of the multi-battery power source  130  of  FIG.  1   . For example, the MCU  530  may select a single-battery mode or a multi-battery mode of operation using any technique described herein. The MCU  530  may generate particular values of the control signals CTR_BAT_ 1 , CTR_BAT_ 2  based on the selected operating mode of the multi-battery power source  130  of  FIG.  1   . 
     In response the control signals CTR_BAT_ 1 , CTR_BAT_ 2 , the drive circuits  510 ,  520  may selectively activate or deactivate the switch devices Q 8 , Q 9 . For example, based on a value of the first control signal CTR_BAT_ 1 , the first drive circuit  510  may activate or deactivate the first switch device Q 8 . Activating the first switch device Q 8  may couple the first battery  132  to the one or more components  102 , and deactivating the first switch device Q 8  may decouple the first battery  132  from the one or more components  102  (e.g., by disconnecting a negative battery terminal of the first battery  132  from the ground node GND). 
     As another example, based on a value of the second control signal CTR_BAT_ 2 , the second drive circuit  520  may activate or deactivate the second switch device Q 9 . Activating the second switch device Q 9  may couple the second battery  134  to the one or more components  102 , and deactivating the second switch device Q 9  may decouple the second battery  134  from the one or more components  102  (e.g., by disconnecting a negative battery terminal of the second battery  134  from the ground node GND). 
     One or more aspects of  FIG.  5    enable selection among a single-battery mode of operation of the portable device  100  and a multi-battery mode of operation of the portable device  100 . As a result, power provided to the one or more components  102  can be selectively increased without involving redesign of certain high-voltage components (as in the case of some series-coupled battery designs) while reducing or avoiding instances of battery-to-battery charging (as in the case of some conventional parallel-configured battery designs). 
       FIGS.  6 A- 6 I  illustrate examples of circuits that may be included in the portable device  100 . In  FIGS.  6 A- 6 I , the circuits include a PM circuit  610 , a bootstrap circuit  620 , a driver circuit  630 , 15 V circuitry  640 , and a switch  650 . In some examples, the switch  650  can be used to implement the first switch device  124 , the second switch device  126 , or both. The circuits of  FIGS.  6 A- 6 I  further include a light-emitting diode (LED) port  655 . In some examples, the LED port  655  is included in a user interface or in a status light device of the portable device  100 . 
     The circuits of  FIGS.  6 A- 6 I  further include a particular non-limiting example of the MCU  530 . The circuits of  FIGS.  6 A- 6 I  further include a hall effect or back electromotive force (hall/BEMF) circuit  680  and a temperature sensor circuit, such as a negative temperature coefficient (NTC) circuit  690 . 
       FIGS.  7 A and  7 B  illustrate examples of devices that may be included in the portable device  100 . The devices of  FIGS.  7 A and  7 B  include a tilt printed circuit board assembly (PCBA)  710 . The tilt PCBA  710  includes a tilt sensor  712  configured to generate an indication (“tilt sense”) of an orientation (e.g., a tilt) of the portable device  100 . In one example, the tilt sensor  712  includes a photo-coupler device. 
     The devices of  FIGS.  7 A and  7 B  further include an LED PCBA  720 . The LED PCBA  720  may be configured to generate an indication (“bat_check”) of a battery status associated with the multi-battery power source  130 . The indication of the battery status may be used to alert a user to recharge the portable device  100 . 
     The devices of  FIGS.  7 A and  7 B  further include a handle key  730 . The handle key  730  may be configured to activate or deactivate the portable device  100 . For example, an on/off key  732  may selectively power-on or power-off the portable device  100 . A lock key  734  may selectively lock the portable device  100  in the power-off mode. In some examples, one or both of the on/off key  732  or the lock key  734  are included in the power-up switch  106  of  FIG.  1   . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 
     Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.