Power supply for battery powered devices

POWER SUPPLY FOR BATTERY POWERED DEVICES

BACKGROUND

0003The present invention relates to power supplies for battery powered devices. It finds particular application to situations in which it is desirable to supplement the energy provided by or otherwise charge the main battery of a battery powered device with energy from an auxiliary battery.

0004Recent years have seen a proliferation of battery powered devices. Digital cameras, personal digital assistants (PDAs), hand held games, portable audio players, remote controls, wireless computer keyboards and mice, portable and remote data communications devices, and mobile telephones are but a few examples.

0005These devices typically include one or more main batteries which power the device during normal operation. Where the main batteries are rechargeable (secondary), the devices are sometimes provided with battery charging circuitry which provides electrical energy for charging the batteries. Depending on the implementation, the charging circuitry may be located either internal or external to the device itself. In any case, the charging circuitry is ordinarily powered from an alternating current (AC) power outlet, a 12 volt direct current (VDC) automobile power outlet, or the like. Consequently, the device must be returned to a fixed or semi-fixed location for charging.

0006So-called hybrid battery management technology, which uses an external auxiliary battery together with associated charge control circuitry, has been, used to provide supplemental power to battery powered devices. In one implementation, the auxiliary battery and charge control circuitry have been housed in a generally cylindrical housing, which has been suspended at one end of a cable, with the other end connected to the positive and negative terminals of the charging or power port of the battery powered device.

0007Figure 1 shows the output current I₀Ut provided to a device having a lithium ion (Li-ion) main battery according to a hybrid battery management technique. Where the main battery voltage is less than a first value, the output current is substantially independent of the main battery voltage. Where the main battery voltage has a relatively higher value, the output current is a substantially linear function of the main battery voltage. Where main battery voltage has had a still higher value, the output current has again been substantially independent of the main battery voltage. As can also be seen in Figure 1, the output current has also been a function of the auxiliary battery voltage.

0008While these techniques have provided for more convenient charging of the device's main battery during mobile operation, there remains room for improvement. In particular, it remains desirable to extend the operating life of the auxiliary battery while minimizing modifications to the battery powered device. In many cases, it is also desirable that the external device have a form factor which complements that of the battery powered device.

0009SUMMARY Aspects of the present invention address these matters, and others.

0010According to a first aspect of the invention, an auxiliary power supply is adapted for use with a battery powered device including first electrical circuitry which presents a time varying electrical load and a first rechargeable battery which provides electrical energy to the first electrical circuitry. The auxiliary power supply includes a battery receiving region adapted to receive a second battery, and second electrical circuitry. The second electrical circuitry receives a signal from the battery powered device. The signal is indicative of the magnitude of the time varying electrical load. The second electrical circuitry also utilizes energy from the second battery to produce a power supply output for recharging the first rechargeable battery and for providing electrical energy to the first electrical circuitry, and adjusts the power supply output as a function of the charge state of the first rechargeable battery, the charge state of the second battery, and the signal. The auxiliary power supply also includes a first electrical connector in operative communication with the second electrical circuitry and adapted to selectively electrically connect the power supply output to the battery powered device. According to another aspect of the invention, an apparatus is adapted to supply electrical energy to a battery powered device including a first, rechargeable battery and first electrical circuitry, wherein the first electrical circuitry receives electrical energy from the first battery and presents a time varying electrical load current during operation of the device. The apparatus includes a first housing which defines a battery receiving region, first and second battery contacts for making electrical contact with a second battery received in the battery receiving region, a first electrical connector in mechanical communication with the first housing and disposed electrically between the second battery and the first electrical circuitry, and second electrical circuitry. The second electrical circuitry receives energy from the second battery, generates an output for supplying electrical energy to the first electrical circuitry and for recharging the first battery, and adjusts the output as a function of the state of charge of the first battery and a signal indicative of the time varying electrical load current.

0011According to another aspect of the invention, a power supply is adapted for use with a battery powered device including first electrical circuitry which presents a time varying electrical load current and a first, rechargeable battery which supplies electrical energy to the first electrical circuitry. The power supply includes a battery receiving region adapted to receive a second battery, means for determining a state of charge of the first battery, electrical circuit means operatively connected to the second battery for supplying electrical energy to the first electrical circuitry and to the first battery, means for receiving a signal indicative of the time varying electrical load current, and an electrical connector disposed electrically between the second battery and the first electrical circuitry. The electrical circuit means produces an output which is a function of the state of charge of the first battery and the time varying electrical load current.

0012According to still another aspect of the present invention, an apparatus includes a battery powered device and a power supply. The battery powered device includes a first housing which defines a first battery receiving region adapted to receive a first, rechargeable battery, and first electrical circuitry disposed in the first housing which receives electrical energy from the first battery and draws a time varying electrical load current. The battery powered device also includes means for providing an electrical signal indicative of the time varying electrical load current, and a first electrical connector operatively electrically connected to the first battery, the first electrical circuitry, and the means for providing. The power supply includes a second housing which defines a second battery receiving region adapted to receive a second battery, means for receiving the signal, and power supply circuitry disposed in the second housing. The power supply circuitry receives electrical energy from the second battery, generates an output for supplying energy to the first electrical circuitry and the first battery, and adjusts the output as a function of the state of charge of the first battery and the signal. The power supply also includes a second electrical connector carried by the second housing. The second electrical connector is operatively electrically connected to the power supply circuitry and the means for receiving.

0013Those skilled in the art will recognize still other aspects of the present invention upon reading and understanding the attached description.

BRIEF DESCRIPTION OF THE DRAWINGS

0015The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: Figure 1 depicts an output current provided by a prior art device.

0016Figure 2 is an electrical block diagram of an auxiliary power supply connected to a battery powered device.

0017Figure 3 is a functional block diagram of an electrical device. Figure 4 is a functional block diagram of an auxiliary power supply. Figure 5 depicts an output current provided by an auxiliary power supply.

0018Figure 6 depicts an auxiliary power supply and a mobile telephone. Figure 7 depicts an auxiliary power supply and a portable entertainment device. Figure 8 depicts steps in the operation of an auxiliary power supply in conjunction with a battery powered device.

DETAILED DESCRIPTION

0020With reference to Figure 2, a battery powered device 100 includes device electrical circuitry 102, one or more main batteries 104, charge control circuitry 106, and a main device electrical connector 108a. The electrical circuitry 102 performs some or all of the functionality provided by the battery powered device 100. Depending on the type of electrical device 100, the electrical circuitry 102 may take any number of forms. For example, the electrical circuitry 102 may perform the electrical functions required of a camera, PDA, mobile phone, game device, bar code reader, computer mouse or keyboard, portable or remote communications device, or the like, although other types of devices 100 and electrical circuitry 102 are contemplated. The device circuitry 102 may also include a communications interface 103 adapted to provide communications with an external device or devices. In one embodiment, the communications interface is a known universal serial bus (USB) communications interface which provides digital communications with external devices, for example an external computer. Other serial, parallel, or analog communications interfaces are also contemplated.

0021In normal operation, the electrical circuitry 102 is powered by one or more main batteries 104. The chemistry, form factor, and number of the batteries 104 employed in a given device 100 are generally dependent on the type of device 100 and the requirements of the electrical circuitry 102. In many cases, however, the battery or batteries 104 are secondary batteries. Examples of currently available secondary battery chemistries Li-ion, nickel metal hydride (NiMH), nickel cadmium (NiCd), Li-ion polymer, and reusable alkaline. Commonly available battery form factors include generally cylindrical batteries such as conventional AAA, AA, C, and D size cells, as well as generally rectangular or prismatic batteries. The main battery 104 may also be a so-called smart battery which - operates according to the known smart battery standard. Other battery chemistries and form factors are also contemplated.

0022The charge control circuitry 106, which provides functionality related to the charging of the main battery or batteries 104, is disposed electrically between the electrical connector 108 and the battery 104. In an implementation which is particularly well suited to devices 100 in which the bulk of the charge control functionality is located external to the device 100, the charge control circuitry includes a diode, transistor, or components which protects the device 100 if the main device connector 108a is shorted, connected to external signals of the incorrect polarity, subjected to an over voltage, or the like. In another implementation, the charge control circuitry 102 may include circuitry which controls the voltage and/or current applied to the battery or batteries 104. Such circuits, which commonly receive power from a power cube connected to the AC mains or an automotive 12 VDC power source, are known to those skilled in the art and are ordinarily implemented based on the desired charging functionality and the characteristics of the battery 104. The charge control circuitry 106 may also be omitted. Some or all of the charge control circuitry 106, the device electrical circuitry 102, and the communications interface (103) may be implemented in a single integrated circuit or application specific integrated circuit (ASIC); they may also be implemented in multiple integrated circuits or discrete components.

0023The main device electrical connector 108a provides removable electrical connections between the device 100 and the external environment. In the exemplary USB interface, the connector 108a is a standard USB connector which provides positive 110_p and negative HO_n electrical power connections, as well as positive 112_P and negative 112_n data connections. The main device connector 108a may also provide other electrical connections relevant to the particular device 100, such as data or memory connections, control connections, or the like. The main device connector 108a may also be implemented as one more physical connectors; such a configuration is particularly useful where it is desirable to allow the device 100 to be independently connected to more than one external device.

0024With ongoing reference to Figure 2, the total current I_0Ut received by the battery powered device 100 through the electrical connector 108a can be expressed as follows: Equation 1

0025H)Ut ^device ' lbatteiy where Idcvicc is the load current drawn by the device circuitry 103 and Ibattπy is the current drawn by the main battery 104. To measure the device load current I_devico a sense resistor 116 may be disposed electrically in series between the device electrical circuitry 102 and the negative 11O_n or positive 110_p power connections. As will be appreciated, the voltage across the sense resistor 116 provides a signal 114 indicative of the load current drawn by the device electrical circuitry 102. The current drawn by the main battery 104 could likewise be determined using an analogous sense resistor in series with the battery 104. Turning now to Figure 3, the device circuitry 102 typically includes a processor 202 such as a microprocessor or microcontroller which executes instructions in an associated memory. The processor 202 coordinates the transfer of data via the communications interface 103 and cooperates with the other device specific circuitry 204 to provide the desired device functionality. The processor 202 also receives information relating to or otherwise controls factors which influence one or more of the device electrical load 206, the device electrical characteristics 208, and the main battery state of health 210. The device electrical load information 206 includes information indicative of one or more of the actual or anticipated power requirements of the device electrical circuitry 102. The measured load 212 includes a measured value of the load presented by the device electrical circuitry 102. In one implementation, the measured load is the value of Idevic_e obtained by measuring the voltage across the sense resistor 116.

0026The actual operating state information 214 includes information relating to the current operating state or mode of the device 100. For example, many devices are characterized by relatively long periods of relatively low power or quiescent operation interspersed with periods of relatively higher power operation. Depending on the nature of the device, the device typically enters a particular operating state in response to an operator input or command or automatically based on another event or criterion. In the case of a mobile telephone, for example, the user may initiate or accept a telephone call, during which time the circuitry 102 places a relatively high load on the main battery 104. Moreover, the power output of the telephone's transmitter may be adjusted based on the strength of the local radio frequency signal, again influencing load placed on the main battery 104. In any case, the operating state or states 214 of the device may in many cases provide a reasonable indication of the load presented to the main battery 104.

0027The anticipated operating state information 216 includes information relating to an anticipated or predicted operating state of the device 100. A portable or remote data communications device, for example, may be programmed to upload or download data at one or more scheduled times during the course of day, week, or other time period. The device 100 may also be programmed to transfer data at desired time intervals (e.g., hourly, daily, or the like), or following the occurrence of certain events. The device 100 may also be programmed to predict future operating states based on the operating history of the device, for example where the user has caused the device to enter a particular operating state at regular times or intervals. In any case, the anticipated operating state 216 may provide a reasonable indication of an anticipated future operating state, and hence an anticipated load to be presented to the main battery 104.

0028The device electrical characteristics 208 include information relating to the power requirements of the device 100. In one implementation, a device identifier 218 or code is stored in a memory associated with the device 100. As one example, the device identifier 218 identifies the manufacturer and model number of the device 100. As another example, the device identifier 218 may identify the device 100 as belonging to a class of devices having similar power requirements. Analogously, a battery identifier 220 may also be used to identify the manufacturer and/or model number of the main battery 104, or otherwise identify the battery as being of a particular class of batteries having similar characteristics. In another implementation, specific battery voltage, current, capacity, chemistry or other characteristics 222 of the device 100 may be provided, either in a memory associated with the device 100 or a memory associated with the main battery 104. The battery state of health 210 includes information indicative of the health of the main battery 104. This information may include information indicative of the battery charge state 224, for example the measured output voltage V_mai_n of the main battery 104. In another example, the charge state may be determined by way of a so called fuel gauge, in which the charge remaining in the main battery is estimated based on the capacity of the battery and a measurement or estimate of the energy drawn from it. Another example of battery health information 210 is a battery temperature 226, which is typically measured using a thermistor of other temperature sensitive device.

0029Returning now to Figure 2, a battery powered auxiliary power supply 150 includes one or more auxiliary batteries 152, power supply circuitry 154, and an auxiliary electrical connector 108b. In one embodiment, and as will be described in greater detail below, the auxiliary power supply 150 is adapted to interface with a number of different main devices 100 having different electrical power requirements. In another embodiment, a family of external power supplies is provided, with the members of the family having different load ratings or capacities.

0030The auxiliary power supply 150 includes a battery receiving region which includes the requisite battery contacts and which accepts one or more auxiliary batteries 152. The chemistry, form factor, and number of the auxiliary batteries 152 employed in a given power supply 150 are generally dependent on the power requirements of the main device or devices 100 with which the external power supply 150 is expected to operate, the desired form factor and portability of the external power supply 150, and like factors. The power supply circuitry 154, which is powered by the auxiliary battery 152, provides electrical energy for powering the device electronics 102 and charging the main battery 104. Also associated with the auxiliary power supply 150 is a communication interface 156. In the illustrated embodiment, the communication interface 156 is a USB interface, although the interface would ordinarily be selected for compatibility with the device or devices 100 with which the auxiliary power supply 150 is expected to operate. Note that the charge control circuit 154 and communications interface 156 may be implemented in one or more integrated circuits, ASICs, or other devices. A sense resistor 120 analogous to the sense resistor 116 provides a signal indicative of the output current Io_Ut being supplied to the battery powered device 110.

0031The power supply connector 108b is adapted to matingly engage the battery powered device connector 108a to provide the power 110_p, 11 O_n and data 112_P, 112_n connections. Turning now to Figure 4, the power supply circuitry 154 includes advantageously includes a processor 302 such as a microprocessor or microcontroller which executes instructions stored in an associated memory. The processor 302 interfaces with the communications interface 156 and with power supply electronics 304, and also receives information relating to one or more of the battery powered device electrical characteristics 306, the battery powered device operating state 308, and main battery state of health 310.

0032The battery powered device electrical information 306 includes information relating to the power and/or load requirements various main devices 100. In one implementation, the voltage, current, or other characteristics of various battery powered devices 100 are contained in a list or database stored in a memory accessible to the processor 302. The device identifier 218 received from a given main device is used to access the relevant information from the memory. In another implementation, the characteristics of various main batteries 104 are stored, with the battery identifier 220 received from a given main device used to access the relevant information. As will be appreciated, these arrangements facilitate the use of the external power supply 150 with battery powered devices 100 or batteries 104 having different power requirements.

0033The main device operating state information 308 includes information relating to the operating states or modes of one or more battery powered devices 100. In one implementation, the voltage, current, or other load requirements associated with the operating states of one or more battery powered devices 100 are included in a list or database stored in the memory. The actual 214 or anticipated 216 operating state information and the device identifier 218 identifier, if applicable, received from a given device 100 are used to access the pertinent information from the memory. Note that some or all of the device electrical characteristics 306 and operating state information 308 may be combined in a single list or database. In the mobile telephone described above, for example, the telephone may include a low power or idle mode and one or more transmit modes, each presenting a different electrical load. Other devices 100 may have different operating modes. As will be appreciated, the actual operating state 216 information may serve as a proxy for the measured load 212. Moreover, the anticipated operating state information 216 provides information which is ordinarily not available or often difficult to infer from the measured load 212 or the actual operating state 216.

0034The main battery state of health 310 includes main battery state of health 210 information received from the battery powered device 100, for example the main battery voltage Vmain. In the embodiment of Figure 2, the main battery voltage can ordinarily determined form the voltage at the positive power connection 110_p. Alternately, the voltage may be obtained from another location. While the main battery state of health information 310 is shown as being provided directly to the power supply electronics 304, the information may also be communicated to the processor 302 via the communications interface 156.

0035The processor 302 is operatively connected to the power supply electronics 304. Various power supply circuits and topologies are known and can be readily implemented by those skilled in the art based on factors such as electrical characteristics of the battery powered device and its batteries. Advantageously, however, the voltage, current, and/or other output characteristics of the power supply electronics 304 are established based on information received from the processor 302. In particular, the processor 302 establishes the voltage and/or current setpoints of the power supply electronics 304 as a function of one or more of the device electrical characteristics 306, the device operating state information 308, and the main battery state of health 310.

0036The auxiliary battery state of health information 312 includes information relevant to the state of health of the auxiliary battery 152. Such information may include charge state information 324 such as a measured auxiliary battery voltage V_aux, the auxiliary battery temperature 326 or other information analogous to that described above in relation to the main battery 104. While the auxiliary battery state of health information 312 is shown as being provided directly to the power supply electronics 304, the information may also be provided to the processor 302. In one implementation, the power supply electronics 304 can be configured to supply a total output current I_0Ut to the battery powered device 100 according to the transfer function of Figure 1 , where the output current lout is a function of the auxiliary battery voltage V_aUχ and the main battery voltage Vmain- However, the energy available from the auxiliary battery 154 may be more effectively utilized by varying or modulating the output of the external power supply 150 as a function of the actual or predicted load presented by the device electronics 102. Figure 5 depicts the output current l_out supplied by the power supply electronics 304 as a function of the main battery voltage Vmain for each of a plurality of device electrical circuit currents Idevi_ce* with Idevice generally increasing from Io to Ie, and where Io represents the load current with the device 100 turned off or in a relatively low power operating mode. In Figure 5, the auxiliary battery voltage V_8Ux is assumed to be constant for ease of illustration, it being understood that the output current l_ou_t is preferably also a function of the auxiliary battery voltage V_aux as depicted generally in Figure 1. As can be seen, the output current supplied by the power supply electronics 304 is, for a given device electrical load I_devi_ce and auxiliary battery voltage V_aUχ, at a maximum value where the main battery voltage V_maj_n is relatively low. The maximum output current lout m_ax is advantageously set at a value which satisfies the following condition:

0037Equation 2 IbatteryO ⁺ ^device ^> hut mnx — *devicc where Ibatteryo is the charge current that would be drawn by the main battery 104 if the current were not otherwise limited.

0038Such an arrangement assures that the external power supply 150 provides sufficient power to operate the battery powered device 100 while still providing energy to charge the main battery 104, albeit at a reduced rate. As discussed more fully above, the device current Idevice may be advantageously obtained by measuring the actual device current or inferred from an actual operating state of the battery powered device 100.

0039The maximum output current I_{oUt maκ} may also be adjusted based on the value of an anticipated device operating state. Thus, where it is expected that the device will become active at a time in the future, the maximum output current may be increased to a level which charges the main battery as quickly as possible, or to a level which is expected to fully charge the main battery 104 before the device 100 enters the higher power operating state. As another example, the user may enter a command to charge the main battery 104 as quickly as possible or otherwise at a relatively faster rate, in which case the value of the maximum output current may be increased accordingly.

0040The output current I_0Ut can be adjusted by causing the processor 302 to vary the value of the sense resistor 120 as a function of the device current Idevice- As will be appreciated, the current feedback is function of the value of the sense resistor 120.Consequently; decreasing the value of the sense resistor 120 increases the output current, while increasing the value decreases the output current. As discussed above, the value of the sense resistor may advantageously be limited to values at which Equation 2 is satisfied. As a result, the output current can be reduced to or held a level that is below the sum of the maximum charge acceptance rate for the main battery 104 and the load presented by the device electrical circuitry 102. Other techniques, such as the use of a programmable gain amplifier at the output of the sense resistor 120, may also be implemented. The power supply electronics 304 may be implemented using the known TECl 03

0041Step-Up Converter and Charge Controller integrated circuit available from Techtium, Ltd. of Tel Aviv, Israel. Other circuits and circuit configurations are also contemplated.

0042Various alternatives are possible. As will be appreciated, the functions implemented in the auxiliary power supply 150 ordinarily depend on the characteristics of or other information available from the battery powered device or devices 100 with which the auxiliary power supply 150 is expected.to operate.

0043Moreover, the battery powered device 100 may also supply the device electrical load information 206 through a signal available at the connector 108a. In one ^■ implementation, a measured value of the device current Idevice may be provided via an analog voltage signal. In another, the actual 214 or anticipated 216 operating state information may be provided via a digital signal. In yet another, the desired signals may be provided in a two wire communications interface in which the signals are superimposed on the power signal, preferably as serial digital signals generated by modulating the voltage and/or current levels. In still another, the battery powered device 100 may supply an output current set point signal .which is a function of the device current In any case, the auxiliary power supply circuitry 154 includes suitable analog and/or digital circuitry for adjusting the value the output current I₀Ut as a function of the signal, for example the adjusting the effective value of the sense resistor 120.

0044As another alternative, the auxiliary battery 152 may be located in the auxiliary power supply 150, with some or all of the power supply circuitry 154 located in the battery powered device 100.

0045The above discussion has focused on providing information which is directly indicative of the load presented by the device electronics 102. In view of Equation 1, however, information indicative of the main battery current lbmay may be provided, as subtracting the battery current hattery from the output current l_olΛ yields information indicative of the load presented by the device electronics 102.

0046Turning now to Figure 6, an exemplary auxiliary power supply 650 is shown with a mobile telephone 600. The phone 600 includes a housing 601 having a front major surface 602, a spaced apart rear major surface, and additional surfaces 604a, 604b, 604c, and 604d. Located on the surface 604a is a female connector 608a. The auxiliary power supply 650 includes a housing 651 having a front major surface 672, a spaced apart rear major surface, and additional surfaces 674a, 674b, 674c, and 674d. The auxiliary power supply 650 houses the power supply circuitry 154 and includes a battery receiving region which is adapted to selectively receive an auxiliary battery 652. A user removable cover 660 (shown in partial cutaway view to expose the battery 652) allows the user to selectively access the battery receiving region. A male connector 608b located on the surface 674a is adapted to matingly engage the female connector 608a. As illustrated, the curvature of the surface 674a substantially conforms to a curvature of the surface 604a, and the width of the housing 601 is approximately equal to the width of the housing 601 at the interface therebetween. Turning now to Figure 7, another exemplary auxiliary power supply 750 is shown with a portable entertainment device 700. The portable entertainment device 700 includes a housing 701 having a front major surface 702, a spaced apart rear major surface, and additional surfaces 704a, 704b, 704c, and 704d.. Located, on the surface 704a is a female connector 708a. The auxiliary power supply 750. includes a housing 751 having a front major surface 772, a spaced apart rear major surface, and additional surfaces 774a, 774b, 774c, and 774d. The auxiliary power supply 750 houses the power supply circuitry 154 and includes a battery receiving region which contains the requisite positive and negative battery terminals and is adapted to selectively receive auxiliary batteries 752. A user removable cover 760 (shown in partial cutaway view to expose the batteries 752) allows the user to selectively access the battery receiving region. A male connector 708b located on the surface 774a is adapted to matingly engage the female connector 708a. As illustrated, the width of the housing 701 is approximately equal to the width of the housing 701 at the interface therebetween.

0047Other arrangements are also possible. For example, the auxiliary power supply may connect to one of the other surfaces of the main device. The auxiliary power supply and the device may also connect via a cable which includes suitable connectors, and may also have a cylindrical or other form factor which does not conform to that of the battery powered device.

0048In operation, the user operates the battery powered device 100 as desired. Of course, continued operation of the device 100 leads to the eventual discharge of the main battery 102. To recharge the battery, the user typically connects the device to a fixed charger.

0049In some situations, such as where a power source required to operate the fixed charger is not readily available, the user may elect to use the external power supply 150. With reference to Figure 8, the user connects the external power supply 150 and the battery powered device 100 through their corresponding electrical connector portions 108a, 108b at step 802.

0050Where the auxiliary power supply 150 and the main device 100 communicate through a USB interface, the devices undergo a USB enumeration process at 804. Once the external power supply 150 is identified as an external power source, the battery powered device may advantageously allow its communication interface 103 to operate outside the USB power standards.

0051If implemented, the battery powered device 100 provides the device electrical characteristics 208 to the external power supply 150 at step 806. At 808j the external power supply 150 uses the device power characteristic 208 to establish the desired voltage and current levels to be applied to the battery powered device 100.

0052At 810, the battery power device 100 provides the device electrical load information 206 to the external power supply 150. As noted above, the load information 206 may be provided by way of a measured value 212. Alternately, or in addition to the measured value 212, actual 214 and/or anticipated 216 operating state information may be transferred. Depending on the implementation, the information may be provided continuously or at various times during operation. At 812, the auxiliary power supply 150 supplies an output voltage and current to the main device. As noted above, the power supply output is preferably a function of the electrical load presented by the device electrical circuitry 103.

0053At 814, the user disconnects the auxiliary power supply 150 from the main device.

0054The invention has been described with reference to the preferred embodiments. Of course, modifications and alterations will occur to others upon reading and understanding the preceding description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.