Abstract:
A system for bi-directional battery charging, including a first electronic device, including a first rechargeable battery, for providing power to the first electronic device, and a first battery charger, and a second electronic device, including a second rechargeable battery, for providing power to the second electronic device, a second battery charger, a voltage boost that receives an input voltage from the first rechargeable battery and is selectively enabled to either up-convert the input voltage as input to the second battery charger, or else to passively pass the input voltage to the second battery charger; and a controller for programmatically controlling the first and the second battery chargers and the voltage boost, wherein the second electronic device attaches to the first electronic device to operate in combination therewith, and wherein the controller is programmed to decide, based on the voltages of the first and the second rechargeable batteries: (i) whether to supply power to the second electronic device from the first or second rechargeable battery, (ii) whether to charge the second rechargeable battery from the first rechargeable battery, and (iii) whether to enable or disable the voltage boost. A method is also described and claimed.

Description:
FIELD OF THE INVENTION 
     The field of the present invention is management of battery power supply and battery charging for electronic devices. 
     SUMMARY OF THE DESCRIPTION 
     Aspects of the present invention relate to battery supply and battery charging of coupled electronic devices. One or both of the electronic devices operates in a standalone mode, and the devices also operate in a coupled mode when one is attached to the other. Each device has its own rechargeable battery and internal battery charger, and the coupling enables the battery of one device to supply power to the other device, and to charge the other device&#39;s battery. Using the present invention, optimized logic for controlling power supply and battery charging of the coupled devices, provides extended operational time. 
     The optimized logic decides when to supply battery power from one battery to the other device, and when to charge one battery from the other, based on the voltages of the two batteries, and based on the operational modes of the two devices. 
     The present invention applies generically to a wide variety of electronic devices that use single or dual input battery chargers, voltage boosts, and USB chargers to power manage their electrical components. In particular, the present invention applies to a small modular cell phone that is attachable to host devices and to jackets with user interfaces. The modular cell phone provides the host devices with wireless communication functionality, when attached thereto. The jackets provide the modular cell phone with custom keypads, displays, microphone, speakers and other such user interface components. The present invention also applies to a small modular media player that attaches to host devices and provides them with media playing functionality. 
     There is thus provided in accordance with an embodiment of the present invention a system for bi-directional battery charging, including a first electronic device, including a first rechargeable battery, for providing power to the first electronic device, and a first battery charger, and a second electronic device, including a second rechargeable battery, for providing power to the second electronic device, a second battery charger, a voltage boost that receives an input voltage from the first rechargeable battery and is selectively enabled to either up-convert the input voltage as input to the second battery charger, or else to passively pass the input voltage to the second battery charger; and a controller for programmatically controlling the first and the second battery chargers and the voltage boost, wherein the second electronic device attaches to the first electronic device to operate in combination therewith, and wherein the controller is programmed to decide, based on the voltages of the first and the second rechargeable batteries: (i) whether to supply power to the second electronic device from the first or second rechargeable battery, (ii) whether to charge the second rechargeable battery from the first rechargeable battery, and (iii) whether to enable or disable the voltage boost. 
     There is further provided in accordance with an embodiment of the present invention a system for bi-directional battery charging, including a first electronic device, including a first rechargeable battery, for providing power to the first electronic device, a first battery charger, a first voltage boost for receiving an input voltage is selectively enabled to either up-convert the input voltage as input to the first battery charger, or else to block the input voltage from being transferred to the first battery charger, and a second electronic device, including a second rechargeable battery, for providing power to the second electronic device and for providing the input voltage to the first voltage boost, a second battery charger, a second voltage boost that receives an input voltage from the first rechargeable battery and is selectively enabled to either up-convert the input voltage as input to the second battery charger, or else to passively pass the input voltage to the second battery charger, and a controller for programmatically controlling the first and the second battery chargers and the first and second voltage boosts, wherein the second electronic device attaches to the first electronic device to operate in combination therewith, and wherein the controller is programmed to decide, based on the voltages of the first and the second rechargeable batteries: (i) whether to supply power to the second electronic device from the first or second rechargeable battery, (ii) whether to charge the first or second rechargeable battery from the other rechargeable battery, and (iii) whether to enable or disable the first and second voltage boosts. 
     There is yet further provided in accordance with an embodiment of the present invention a method for controlling battery power supply and battery charging for two coupled electronic devices, each device having its own rechargeable battery and its own internal battery charger, including determining battery voltages for each of the two electronic devices, determining operational modes for each of the two electronic devices, and based on the determining battery voltages and the determining operational modes, controlling the batteries and battery chargers including deciding (i) whether to supply power to each electronic device from its own battery or from the other device&#39;s battery, and (ii) whether to charge one battery from the other battery. 
     There is additionally provided in accordance with an embodiment of the present invention a system for bi-directional battery charging, including two coupled electronic devices, each device comprising a rechargeable battery and an internal battery charger, wherein the rechargeable battery of each device is able to supply power to both devices, and wherein the rechargeable battery of each device is able to charge the other device&#39;s rechargeable battery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1A  is a simplified block diagram of a modular cell phone connected to a jacket, in accordance with an embodiment of the present invention; 
         FIG. 1B  is a simplified block diagram of a modular cell phone connected to a host, in accordance with an embodiment of the present invention 
         FIG. 2  is a mechanical drawing with cross-sectional views of a modular cell phone, in accordance with an embodiment of the present invention; 
         FIG. 3  is an illustration of a jacket for a modular cell phone, in accordance with an embodiment of the present invention; 
         FIG. 4  is an illustration of a modular cell phone being inserted into a jacket, in accordance with an embodiment of the present invention; 
         FIG. 5  is an illustration of a modular cell phone being inserted into a host device, in accordance with an embodiment of the present invention; 
         FIG. 6  is a simplified block component diagram of a modular cell phone, in accordance with an embodiment of the present invention; 
         FIG. 7  is a simplified block component diagram of a jacket for a modular cell phone, in accordance with an embodiment of the present invention; 
         FIG. 8  is a simplified block component diagram of a host device that interoperates with a modular cell phone, in accordance with an embodiment of the present invention; 
         FIG. 9  is a simplified block diagram of bi-directional battery charging for a jacket or a simple host device, in accordance with an embodiment of the present invention; 
         FIG. 10  is a summary of bi-directional battery charging logic for the hardware of  FIG. 9 , in accordance with an embodiment of the present invention; 
         FIG. 11  is a simplified block diagram of bi-directional battery charging for a complex host device, in accordance with an embodiment of the present invention; and 
         FIG. 12  is a summary of bi-directional battery charging logic for the hardware of  FIG. 11 , in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present invention relate to a small modular cell phone that connects to other devices and enables the other devices to communicate wirelessly. The modular cell phone of the present invention operates both in standalone mode as a standalone phone, and also in conjunction with devices to which it is connected. 
     There are two general types of devices into which the modular cell phone may be connected; namely, jackets and hosts. A jacket is a device that provides a user interface for the modular cell phone, and does not operate independently, when not connected to the modular cell phone. A jacket is a device that enriches the capabilities of the modular cell phone, and is not able to operate independently when it is not connected to the modular cell phone. Conversely, a host is a device that is able to operate independently when it is not connected to the modular cell phone, and whose capabilities are enriched by the modular cell phone when connected thereto. 
     Reference is now made to  FIG. 1A , which is a simplified block diagram of a modular cell phone  100  connected to a jacket  200 , in accordance with an embodiment of the present invention. Generally, modular cell phone  100  is inserted inside jacket  200 , and connects therewith by means of a dedicated connector  400 . 
     Reference is now made to  FIG. 1B , which is a simplified block diagram of modular cell phone  100  connected to a host  300 , in accordance with an embodiment of the present invention. Modular cell phone  100  may be attached to host  300  or inserted therewithin, and connects therewith by means of a dedicated connector  400 . Although  FIGS. 1A and 1B  appear similar at this low level of detail, higher levels of detail in  FIGS. 2-8  distinguish between jackets and hosts. 
     Reference is now made to  FIG. 2 , which is a mechanical drawing with cross-sectional views of modular cell phone  100 , in accordance with an embodiment of the present invention. Shown in  FIG. 2  are front, back, left side, right side and top views of modular cell phone  100 . The dimensions of modular cell phone  100  are 72.09 mm×37.59 mm×7.80 mm. It will be appreciated by those skilled in the art that the present invention is applicable when modular cell phone  100  is designed with other dimensions, as well. 
     Reference is now made to  FIG. 3 , which is an illustration of jacket  200  for a modular cell phone, in accordance with an embodiment of the present invention. Jacket  200  shown in  FIG. 3  includes a user interface for an audio/video player. Specifically, jacket  200  includes a USB connector  240 , a keypad  250 , a display  255 , a microphone  260  (shown in  FIG. 7 ), speakers  265 , speaker amplifier  275  (shown in  FIG. 7 ), an earpiece  285 , an earpiece amplifier  290  (shown in  FIG. 7 ) and a headset audio jack  295 . 
     It will be appreciated by those skilled in the art that the components of jacket  200  in  FIG. 3  are illustrative of one jacket design, and that the present invention is applicable to a wide variety of jacket designs. 
     Reference is now made to  FIG. 4 , which is an illustration of modular cell phone  100  being inserted into jacket  200 , in accordance with an embodiment of the present invention. 
     Reference is now made to  FIG. 5 , which is an illustration of a modular cell phone  100  being inserted into host device  300 , in accordance with an embodiment of the present invention. 
     Reference is now made to  FIG. 6 , which is a simplified block component diagram of modular cell phone  100 , in accordance with an embodiment of the present invention. Modular cell phone  100  includes five primary components, as follows: an ASIC controller  105 , a memory storage  110 , a baseband modem  115  for sending and receiving voice communications, an audio/video subsystem  120 , and cell phone charging circuitry  125  for a battery  130 . 
     ASIC controller  105  executes programmed instructions that control operation of mobile communication device  100 . Baseband modem  115  includes a radio frequency (RF) interface  135  that is connected to an antenna. 
     Audio/video subsystem  120  includes a voice, audio and video interface. Cell phone charging circuitry  125  includes a power management integrated circuit. In accordance with an embodiment of the present invention, cell phone charging circuitry  125  supports fixed current and fixed voltage operational modes, and is capable of measuring voltage and current. Cell phone charging circuitry  125  is controlled by controller  105 . 
     Modular cell phone  100  includes a USB interface  140  and an interface  145  for connector  400 . Modular cell phone  100  optionally includes a keyboard  150 , a display  155  and a SIM card  160 . 
     Modular cell phone  100  can be operated in standalone mode, or in conjunction with jacket  200  or host  300  when it is attached thereto. 
     Reference is now made to  FIG. 7 , which is a simplified block component diagram of jacket  200  for modular cell phone  100 , in accordance with an embodiment of the present invention. Jacket  200  includes a controller  205 , jacket charging circuitry  225  and battery  230 , and a USB connector  240 . Jacket charging circuitry  225  supports both a fixed voltage mode and a fixed current mode. Jacket charging circuitry  225  independently controls internal current and voltage of jacket  200 . 
     Jacket  200  provides a variety of user interface components for modular cell phone  100 , including keyboard  250 , display  255 , microphone  260 , respective left and right speakers and left and right speaker amplifiers  265 ,  270 ,  275  and  280 , earpiece  285  and earpiece amplifier  290  and headset audio jack  295 . 
     Jacket  200  supports audio and USB signals being routed to jacket headset port  295 , jacket earpiece  285 , one or two jacket speakers  265  and  270 , and jacket USB connector  240 . Jacket  200  supports stereo amplifiers  275  and  280 , with high impedance inputs and outputs for driving 8Ω speakers  265  and  270 . The circuitry in jacket  200  also supports earpiece amplifier  290 , with a high impedance input and output capable of driving 32Ω speaker  285 . Jacket  200  includes an external interface  245  for connecting jacket  200  to modular cell phone  100  via connector  400 . 
     Reference is now made to  FIG. 8 , which is a simplified block component diagram of host device  300  that interoperates with modular cell phone  100 , in accordance with an embodiment of the present invention. Host device  300  includes four interconnected primary components; namely, a controller  305 , a storage unit  310 , host charging circuitry  325  for a battery  330 , and a USB interface  340 . Host device  300  includes an optional audio/video subsystem  320 . 
     Host device  300  also includes a user interface  350 . User interface  350  may include some of all of the voice, audio and video interfaces shown in  FIG. 7  with reference to jacket  200 . Host device  300  includes an external interface  345  for connecting host device  300  to modular cell phone  100  via connector  400 . 
     Reference is now made to  FIG. 9 , which is a simplified block diagram of bi-directional battery charging for a jacket or a simple host device, in accordance with an embodiment of the present invention. Shown in  FIG. 9  are cell phone controller  105 , cell phone charging circuitry  125  and cell phone battery  130  from  FIG. 6 . Cell phone charging circuitry  125  has a dual input. A first input is connected to USB connector  140  for a USB charger  165 , and a second input is connected to the output of a voltage boost  170 . 
     Also shown in  FIG. 9  are jacket controller  205 , jacket charging circuitry  225 , and jacket battery  230 . Jacket charging circuitry  225  is a single input charger, with its input connected to USB connector  240  for a USB charger  265 . 
     Connector  400  provides signal paths between components of cell phone  100  and components of jacket  200 . Via connector  400 , the input of USB charger  265 , denoted by Vbus in  FIG. 9 , is routed to USB charger  165 . 
     Controller  105  is able to track the voltage on battery  230 , either by directly measuring a battery pin on connector  400 , or by receiving notifications from jacket charging circuitry  225  via connector  400 . 
     Voltage boost  170  receives a standard battery voltage as input and generates as output a minimal charging voltage of cell phone charging circuitry  125 . Typical input to boost  170  is in the range 2.7V-4.2V, and typical output is 4.7V. When enabled, boost  170  up-converts its input voltage. When disabled, boost  170  simply passes its input voltage through to its output, minus any internal voltage drop. Boost  170  is enabled by controller  105  via an enable signal. The input of boost  170  is connected to a pin of connecter  400 , such that when attached to jacket  200 , boost  170  has a direct connection to battery  230 . 
     The system of  FIG. 9  applies advantageously to simple devices  200 , which have limited power consumption, lower than a threshold current, typically 500 mA. In such case, battery  130  supplies current to the electronic components of device  200  through connector  400 . 
     It will be appreciated by those skilled in the art that the bi-directional battery charging diagram in  FIG. 9  applies to a general setting whereby a mobile device can be docked to an accessory device. For the sake of clarity, the above disclosure has been presented for a cell phone that attaches to a jacket. However, the present invention may be used advantageously for bi-directional battery charging for general electronic devices that include controllers, rechargeable batteries, boosts and battery chargers as shown in  FIG. 9 . To this end, the logic provided in  FIG. 10  hereinbelow is disclosed in terms of a mobile standalone device and a docked device, to address the general setting. 
     Reference is now made to  FIG. 10 , which is a summary of bi-directional battery charging logic for the hardware of  FIG. 9 , in accordance with an embodiment of the present invention. For purposes of generality, in the notation of  FIG. 10  cell phone  100  is referred to as a standalone (SA) device, and jacket  200  is referred to as a jacket (JKT), into which the SA device can be docked. 
       FIG. 10  is divided into six columns. The first column refers to a state of the SA battery, and the second column refers to a state of the jacket battery. Referring to  FIG. 9 , the following notation is used in these two columns.
         CC is the charging current for the SA battery. CC should conform to the maximal charging current authorization set by the JKT, and is typically between 200 mA-500 mA. For example, if the SA battery has a charge of 500 mAh, charging with a current greater than 500 mA may be harmful to the battery.   JKT is the voltage of the JKT battery.   SA is the voltage of the SA battery.   STBC is the average standby current of the SA device. STBC is typically between 5 mA-50 mA.   Vc is the voltage drop across the SA boost, the SA battery charger and the SA battery, when being charged with charge CC. Vc is typically approximately 0.3V and corresponds to 50%-100% of the SA battery capacity.   Vh is the maximal voltage to which the SA battery is charged when being charged from the JKT battery. Vh is typically between 3.7V-4V corresponding to approximately 50% capacity of the SA battery.   Vl is the minimal voltage for the SA battery, below which charging from the JKT is forced. Vl is typically between 3.4V-3.5V corresponding to approximately 10% capacity of the SA battery.   Vm is the minimal voltage for the JKT battery, below which charging from the SA device is forced. Vm is typically between 3.4V-3.5V corresponding to approximately 10% capacity of the JKT battery.       

     The third column in  FIG. 10  refers to the mode in which the SA device is operating. There are three operational modes for the SA device, as follows:
         I. High Current Consumption. This mode occurs when the SA device is active and transmitting between the SA device and a base transceiver station (BTS). In this mode the SA has a typical current consumption greater than 100 mA, with peak currents possibly greater than 1 A, depending on power requirement factors, such as the distance of the SA device from the BTS. Using the JKT battery to supply the SA device is undesirable in this mode, due to the high peak currents. Transfer of such high current over connectors poses difficult requirements on the quality and current drive of the JKT battery, boost current and charger current, resulting in increased cost and size of the hardware. Charging in this mode is limited to fixed current, since fixed voltage charging draws peak currents from the JKT, which is undesirable.   II. Standby Current Consumption. This mode occurs when the SA device is not communicating with the BTS. In this mode the SA device has an typical current consumption less than 100 mA, and no peak currents above 100 mA. Such current levels are suitable for supply from the JKT battery, and do not impose limitations on charging.   III. Shutdown. In this mode the SA device is shut down and has negligible current consumption.       

     The fourth column in  FIG. 10  refers to the mode of charging the batteries. There are five charging modes, as follows:
         I. No Charge. The SA battery supplies all SA current. Efficiency is high, since no extra conversion is applied. The SA battery is being depleted during this mode.   II. Supply from JKT Battery. In this mode, the JKT battery supplies current. Efficiency is lower than in the No Charge mode, due to voltage drop on the SA boost and SA charger, but in general this mode is efficient and preserves power of the SA battery for standalone operation of the SA device.   III. Supply from SA and JKT Battery. In this mode, when there are peaks, the current is drawn from both the SA and the JKT battery. When there are not peaks, the current is drawn from the JKT battery alone. Current peaks are prevalent in many wireless communication systems, including inter alia Global System for Mobile Communication (GSM), General Packet Radio System (GPRS), Code Division Multiple-Access (CDMA), and Integrated Digital Enhanced Network (IDEN). For the GSM system, peaks occur due to time division multiplexing and are caused by time slots usage.   IV. Charge from JKT Battery. In this mode the JKT battery charges the SA battery. This mode is inefficient, in some circumstances possibly less than 500% efficiency. If the SA boost is enabled, the efficiency is even lower, by approximately 100%. When the JKT battery is empty, charging from the JKT battery is disabled.   V. Charge from SA Battery. In this mode the SA battery charges the JKT battery. This mode is inefficient, in some circumstances possibly less than 50% efficiency. If the JKT boost is enabled, the efficiency is even lower, by approximately 100%.       

     The fifth column in  FIG. 10  refers to enablement of disablement or the SA boost. The sixth column in  FIG. 10  refers to the SA charger. 
     The logic in  FIG. 10  is implemented as programming logic for SA and JKT battery chargers and SA boost, to optimize their operation. The logic in  FIG. 10  prescribes columns 4-6 (charging mode, SA boost enablement and SA charger) in terms of columns 1-3 (SA battery voltage, JKT battery voltage and SA operational mode). For example, referring to the first two rows in  FIG. 10 , if JKT&gt;SA&gt;Vh and if the SA device is in Standby Current Consumption mode, then the charging mode is set for the JKT battery to supply current to the SA device, the SA boost is disabled, and the SA charger is set to fixed voltage level. If instead the SA device is in High Current Consumption mode, then the charging mode is set for both the SA and JKT battery to supply current to the SA device, and the SA charger is set to fixed current level. The logic in  FIG. 10  optimizes usage of the SA and JKT batteries, in order to provide extended operation time for the SA device in combination with the JKT, and in standalone mode; and in order to facilitate charging the SA battery from JKT. 
     Reference is now made to  FIG. 11 , which is a simplified block diagram of bi-directional battery charging for a complex host device, in accordance with an embodiment of the present invention. Shown in  FIG. 11  are cell phone controller  105 , cell phone charging circuitry  125  and cell phone battery  130  from  FIG. 6 . Cell phone charging circuitry  125  has a dual input. A first input is connected to USB connector  140  for a USB charger  165 , and a second input is connected to the output of a voltage boost  170 . 
     Also shown in  FIG. 11  are controller  305 , host charging circuitry  325 , and host battery  330 . Host charging circuitry  325  has a dual input. A first input is connected to USB connector  340  for a USB charger  365 , and a second input is connected to the output of a voltage boost  370 . Host charging circuitry  325  is a hardware-based charging controller that controls charging, including constant current charging and constant voltage charging, based on its input voltage levels and its output HST battery status. 
     Connector  400  provides signal paths between components of cell phone  100  and components of host  300 . Via connector  400 , the input of USB charger  365 , denoted by Vbus in  FIG. 11 , is routed to USB charger  165 . 
     Controller  105  is able to track the voltage on battery  330 , either by directly measuring a battery pin on connector  400 , or by receiving notifications from host charging circuitry  325  via connector  400 . 
     Voltage boosts  170  and  370  receive standard battery voltage as input and generate as output a minimal charging voltage of cell phone charging circuitry  125  and host charging circuitry  325 , respectively. Typical inputs to boosts  170  and  370  are in the range 2.7V-4.2V, and typical outputs are 4.7V. 
     When enabled, boosts  170  and  370  up-convert their input voltages. When disabled, boost  170  simply passes its input voltage through to its output, minus any internal voltage drops. When disabled, boost  370  blocks its input voltage from going out as output. 
     In an alternative embodiment of the present invention, host controller  305  enables and disables host charging circuitry  325 , and boost  370  operates similarly to boost  170 ; namely, when disabled, boost  370  passes its input voltage through to its output, minus any internal voltage drops. 
     Boost  170  is enabled by controller  105  via an enable signal. The input of boost  170  is connected to a pin of connecter  400 , such that when attached to host  300 , boost  170  has a direct connection to battery  330 . Similarly, boost  370  is enabled by controller  305  via an enable signal. The input of boost  370  is connected to a pin of connector  400 , such that when attached to cell phone  100 , boost  370  has a direct connection to battery  130 . 
     In yet another alternate embodiment of the present invention, host controller  305  enables and disables host charging circuitry  325 , and boost  370  is eliminated. Instead of enabling and disabling a voltage boost, controller  305  enables host charging circuitry  325  when charging is desired, and disables host charging circuitry  325  when charging is not desired. 
     The system of  FIG. 11  applies advantageously to complex devices  300 , which have current consuming components above a threshold current, typically 500 mA. For such devices, it is impractical to supply their current from battery  130 . Such current would require too much draw from battery  130 , and would be too high for transfer over connector  400 . Instead, battery  330  supplies current for the components of device  300 . 
     As mentioned above with reference to  FIG. 9 , it will be appreciated by those skilled in the art that the bi-directional battery charging diagram in  FIG. 11  applies to a general setting whereby a mobile device can be docked to an accessory device. For the sake of clarity, the above disclosure has been presented for a cell phone that attaches to a host. However, the present invention may be used advantageously for bi-directional battery charging for general electronic devices that include controllers, rechargeable batteries, boosts and battery chargers as shown in  FIG. 11 . To this end, the logic provided in  FIG. 12  hereinbelow is disclosed in terms of a mobile standalone device and a docked device, to address the general setting. 
     Reference is now made to  FIG. 12 , which is a summary of bi-directional battery charging logic for the hardware of  FIG. 11 , in accordance with an embodiment of the present invention. As with  FIG. 10 , for purposes of generality, in the notation of  FIG. 12  cell phone  100  is referred to as a standalone (SA) device, and host  300  is referred to as a host (HST) device, into which the SA device can be docked. The notation indicated above for  FIG. 10  applies to  FIG. 12  as well, with HST being used for the docking device instead of JKT. 
     The logic in  FIG. 12  is implemented as programming logic for SA and HST battery chargers to optimize their operation.  FIG. 12  uses the same six columns as  FIG. 10 , with an additional column for indicating enablement/disablement of the HST charger and boost. The logic in  FIG. 12  prescribes the settings in columns 4-7 (charging mode, SA boost enablement, SA charger, HST charger and boost) based on the states in columns 1-3 (SA battery voltage, HST battery voltage and SA operational mode). For example, referring to the first two rows in  FIG. 12 , if HST&gt;SA&gt;Vh and if the SA device is in Standby Current Consumption mode, then the charging mode is set for the HST battery to supply current to the SA device, the SA boost is disabled, the SA charger is set to fixed voltage level, and the HST charger and boost are disabled. If instead the SA device is in High Current Consumption mode, then the charging mode is set for both the SA and HST battery to supply current to the SA device, and the SA charger is set to fixed current level. The logic in  FIG. 12  optimizes usage of the SA and HST batteries, in order to provide extended operation time for the SA device in combination with the HST, and in standalone mode; and in order to facilitate charging the SA battery from the HST. 
     It will be appreciated by those skilled in the art that the distinction of JKT vs HST in the systems of  FIGS. 9 and 11  and in the logic of  FIGS. 10 and 12  is merely for the purpose of clarity of exposition. The system and logic of  FIGS. 9 and 10  also apply to simple host devices  300 , in addition to jackets  200 ; and the system and logic of  FIGS. 11 and 12  also apply to complex jackets  200 , in addition to host devices  300 . In general, the system and logic of  FIGS. 9 and 10  apply to devices (jackets or hosts) with limited power consumption; e.g., less than 500 mA; and the system and logic of  FIGS. 11 and 12  apply to devices (jackets or hosts) with higher current consumption. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific exemplary embodiments without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.