WO2017212245A1

WO2017212245A1 - Methods and apparatus for monitoring electricity storage systems

Info

Publication number: WO2017212245A1
Application number: PCT/GB2017/051632
Authority: WO
Inventors: Robin Shaw; Stephen Irish
Original assignee: Hyperdrive Innovation Limited
Priority date: 2016-06-06
Filing date: 2017-06-06
Publication date: 2017-12-14
Also published as: GB201609867D0; GB2551139A; GB2551139B

Abstract

A state of charge indicator apparatus configured to provide an indication of state of charge of a battery module is disclosed herein, wherein the battery module(100) comprises a battery (108) comprising at least one battery cell. The apparatus comprises a charge determiner (102) configured to determine the state of charge of the battery, a data store (106). The apparatus may also comprise a controller (104) arranged to obtain an indication of state of charge from the charge determiner (102), store the indication in the data store (106) in the event that the charge determiner (102) is powered down, and to determine a substitute indication of the state of charge based on the stored indication in the event that the charge determiner (102) is powered up.

Description

Methods and Apparatus for Monitoring Electricity Storage Systems

This invention relates to methods and apparatus related to storage of electrical energy, and in particular to battery controllers and battery control methods, and in particular to battery control methods and apparatus for monitoring state of charge in a battery.

Generally, systems of power cells or batteries are provided with monitoring systems arranged to provide indications of various parameters of the cells or batteries. In particular, an indication of the state of charge of a battery may be provided to allow a user or external apparatus to gauge or calculate how much power may be derived from the battery before recharging or replacement of the battery will be required.

In some cases, however, the very act of providing a state of charge reading can deplete the battery. In order to provide up to date information on the state of charge of a battery, such readings must be taken regularly. Such measurements, while useful in principle, can therefore be highly counterproductive as they deplete the energy stored in the battery.

Moreover, existing state of charge indicators typically must remain on at all times in order to provide an accurate state of charge value. This is because when they are switched off and on, the charge indicator may forget is previous state of charge value and may reset its state of charge counter to a reset value. The state of charge value provided by such existing state of charge indicators can therefore be very inaccurate if they have been switched off, for example to conserve the energy stored in a battery when not in use.

Aspects of the disclosure are as set out in the appended claims.

Aspects of the disclosure will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic of an example battery module; and

Fig. 2 shows a flow chart illustrating a method of operation of a battery module such as the battery module of Fig. 1 ;

Fig. 3 shows a schematic of another example battery module.

As shown in Fig. 1 , aspects of the present disclosure may provide a method and apparatus for providing an indication of a state of charge of a battery module 100. Aspects of the disclosure may provide a method and apparatus for providing a more accurate estimate of the state of charge of a battery module, such as the battery module 100 shown in Fig. 1 , for example when a component of a battery module such as a charge determiner 102 has been switched off.

Aspects of the disclosure may store a value of the state of charge, and use the stored value of the state of charge as a substitute state of charge if a charge determiner 102 has been switched off and back on again.

Fig. 1 shows a battery module 100 in which a method of the present disclosure can be implemented to provide an indication of state of charge of a battery. The battery module 100 comprises a battery 108 comprising three battery cells coupled to two terminals 110. A charge determiner 102 is coupled in series to the battery 108 between one of terminals 110 and the battery 108. A controller 104 is coupled to the charge determiner 102, and a data store 106 is coupled to the controller 104.

The charge determiner 102 is configured to determine the state of charge of the battery 108 based on a characteristic of the at least one battery cell; a determination of the current delivered by or and/or to the battery 108; and a selected switch-on value.

The charger determiner 102 is configured to provide an indication of state of charge to the controller 104. For example, the charge determiner 102 may be arranged to sense the flow of current through the series of cells 108 to the terminals 110. For example, the charge determiner 102 may act as a coulomb counter.

The charge determiner 102 is also configured to use a selected on value as an estimate of the state of charge each time it is switched on - that is to say, at the point the charge determiner 102 is switched on it assumes that the battery 108 is at a selected state of charge, for example fully charged.

The controller 104 is configured to obtain an indication of state of charge from the charge determiner 102, store the indication in the data store 106 in the event that the charge determiner 102 is powered down, and to determine a substitute indication of the state of charge based on the stored indication in the event that the charge determiner is powered back up. The substitute indication may be provided by using the stored state of charge as the substitute in the first instance (for example, immediately on power up) and then later updating this stored state of charge based on current and/or voltages of the battery 108 during use.

As shown in Fig. 2, in operation, the battery module 100 stores 201 an indication of state of charge provided by the charge determiner 102 in the event that the charge determiner 102 is powered down (for example switched off). In the event that the charge determiner 102 is powered up again (switched back on), a substitute indication of the state of charge is provided in preference to the state of charge provided by the charge determiner 102. The substitute state of charge is however determined based on the stored state of charge, which may be updated to account for usage of the battery 108.

For example, in response to the controller 104 detecting that the charge determiner 102 is being powered down (for example, the controller 104 may receive a data signal or command instructing the controller 104 to power down the charge determiner 102, or the controller 104 may make a determination itself to power down the charge determiner 102 to save energy), the controller 104 is configured to store the most recent state of charge value in the data store 106. Additionally or alternatively, the controller 104 may be configured to routinely store a charge value in the data store 106, for example at intervals such as on a periodic basis or when changes in state of charge pass selected thresholds, for example the state of charge changes by a selected percentage such as 1 % of maximum state of charge.

In response to the charge determiner 102 being powered up (for example turned on) again, the state of charge value provided by the charge determiner 102 resets to a selected value as described above (for example fully charged), which will almost certainly be the incorrect value.

Instead of providing an inaccurate state of charge value, the controller 104 retrieves the state of charge value from the data store 106, and provides a substitute indication of the state of charge based on that stored value rather than the value provided by the charge determiner 102.

The substitute indication of the state of charge is based on the stored state of charge. The substitute indication of the state of charge may be improved for example by updating it based on real-time changes in the state of charge. For example, the stored state of charge value used as the basis for the substitute state of charge may be updated to account for the charging and discharging of the battery 108. For example, the controller 104 may use an indication of the current in/out of the battery 108 to update the stored state of charge. For example, the current in/out of the battery may be sensed by the charge determiner 102 and the controller 104 may obtain associated data/signals from the charge determiner 102. The change in state of charge can be calculated by the controller 104, for example, by taking a series of current measurements and aggregating the measurements over time. This is qualitatively similar to mathematical integration, but carried out in a discrete time implementation, for example based on discrete samples of the current. The stored state of charge value may be updated by simple addition or subtraction of a measured change in charge in the battery 108.

The state of charge value provided by the charge determiner 102 may also be calculated and updated in a similar way. For example, the charge determiner 102 may use the selected switch on value and the sensed current flowing into or out of the battery 108 to update its estimate of the state of charge.

The charge determiner 102 may also be configured to store data describing a characteristic of the battery cells, for example in a data store, such as data store 106. The charge determiner 102 may be configured to use the stored data describing a characteristic of the battery cells to improve the quality of its estimate of the state of charge - for example, rather than simply performing a straightforward accumulation of measured current in/out of the battery 108, the charge determiner 102 takes into account the charging and/or discharging characteristic of the battery 108 as dependent upon parameters comprising at least one of: battery cell voltage; battery and/or cell state of charge; rate of charging or discharging; and a temperature of the battery cells. It will be appreciated that in such examples the battery module 100 may comprise sensors to obtain such parameters, for example a temperature sensor coupled to the battery 108 or a voltage sensor configured to provide a voltage signal. Such parameters may themselves be determined by the battery chemistry, and/or features of its construction and assembly. The charge determiner 102 may also be configured to determine when a charge and/or discharge cycle has completed, and use this information as part of its determination of the state of charge of the battery 108.

In some examples, the indication of state of charge determined by the charge determiner 102 may be based on updating the selected switch on value and an aggregation over time, such as an integral, of a series of measurements of electric current delivered by and/or to the battery 108. The charge determiner 102 may comprise a data store, such as data store 106, storing characteristic data defining the charge/discharge characteristics of the battery 108 and the aggregation is based on the characteristic data.

Additionally or alternatively, the controller 104 may be coupled to a voltage determiner, such as a voltage follower, to estimate a change in state of charge of the battery 108. For example, the controller 104 and/or battery voltage determiner may use a look up table or other kind of association (for example stored in a data store such as data store 106) which provides a mapping of battery voltage to state of charge. The controller 104 may use the estimated change in state of charge of the battery 108 to update the stored state of charge value.

In some examples, the indication of state of charge determined by the charge determiner 102 may be based on both a voltage of the battery 108 and an aggregation over time, such as an integral, of a series of measurements of electric current delivered by and/or to the battery 108.

The calculation used by the controller 104 to update the stored value of the state of charge may be less accurate than the measurement or calculation used to determine the state of charge by the charge determiner 102. This difference may mean that the stored value deviates from the correct value. This deviation may cause the accuracy of the two values to diverge - the value provided by the charge determiner 102 may become more accurate with time, while the stored (and optionally updated) value of the state of charge used as the basis for the substitute indication of the state of charge may become less accurate. This effect may be more noticeable once a number of charge/discharge cycles have completed, for example because the charge determiner's 102 calculation of the state of charge may improve once a number of charge/discharge cycles have completed.

As shown in Fig. 2, the substitute indication of the state of charge is used in preference to the value provided by the charge determiner 102, and may continue to be used in preference to the value provided by the charge determiner 102 until a selected condition 205 is met, which may for example correspond to when the estimate provided by the charge determiner 102 is more accurate than the substitute indication of the state of charge based on the stored state of charge.

For example, the selected condition may be a selected amount of time and/or a selected number of charge/discharge cycles. In some examples, the charge determiner 102 may be configured to provide an indication that it is now able to supply a sufficiently accurate value. At this point, the supplied state of charge value may transition from the substitute indication to the value provided by the charge determiner 102, which as noted above, may be more accurate than the substitute indication provided based on the stored state of charge.

In some examples, the selected condition is based on comparing the substitute indication and the indication provided by the charge determiner 102. In some examples, the selected condition comprises the substitute indication and the indication provided by the charge determiner 102 matching to within 10% of the substitute indication. In some examples the selected condition is the receipt of a message from the charge determiner 102.

The controller 104 may be provided with a communications interface (not shown) to output the state of charge to other equipment such as a charger or a product into which the battery module 100 is installed. For example charging apparatus may require knowledge of the state of charge to stop charging the cells when they have reached a maximum charging value. In some examples, the controller 104 is configured to transmit a network message comprising a unique identifier of the battery module 100 and an indication of the state of charge selected from one of the substitute indication and the indication provided by the charge determiner. In some examples, the state of charge value may be provided to a user for example using a visual indicator or other human readable indication, for example on a display carried by the battery module 100.

Devices requiring power can be connected to the terminals 1 10 to draw power from the battery 108. In the event that a single battery module 100 provides insufficient power on its own, additional battery modules 100 can be connected to the terminals 1 10 of the battery module 100, either in series or parallel to provide a higher current and/or voltage. Alternatively, a charging device can be connected to the connectors 1 10 to recharge the cells of the battery 108 of the battery module 100.

In some examples, the charge determiner 102 may be configured to obtain data describing a characteristic of the battery cells, for example the charge determiner 102 may be configured to perform a lookup operation, for example by making an enquiry to the controller 104 and/or data store 106, for example by sending a data signal to the controller 104 or data store 106.

In some examples, the controller 104 may be configured to store an association between cell voltage and state of charge, and the controller 104 is configured to obtain a cell voltage signal and to use the cell voltage signal and the stored association to determine the substitute indication of state of charge. Another aspect of the disclosure provides an apparatus for providing an indication of state of charge of a battery module, such as the battery module 40 shown in Fig. 3. The battery module 400 comprises a battery 408 comprising a plurality of energy storage cells and coupled to two terminals 410, and a battery management system 404 coupled across the battery 408. The battery module 400 also comprises a charge determiner 402 coupled in series to the battery management system 404 and the battery 408.

As for the battery module 100 described above in relation to Fig. 1 , the battery module 400 may be a sealed container, for example a sealed box. The terminals 410 may be carried by the battery module 400, for example carried by the sealed box, for example on the outside of the sealed box.

The charge determiner 402 is configured to determine a state of charge of the battery 400. The battery management system 404 is configured to switch between an active mode in which it operates to balance the cells of the battery 408 and a sleep mode, wherein the sleep mode consumes less power than the active mode. The battery module 400 is configured so that, when the battery management system 404 switches to the sleep mode, power is maintained in the charge determiner 402.

In some examples, such as in the example shown in Fig. 3, the charge determiner 402 is configured to sense a voltage across a cell of the battery 408. As shown in Fig. 3, the charge determiner 402 may be coupled to a plurality of voltage determiners 412, such as a voltage follower, which are each coupled across a respective cell of the battery 408. The charge determiner 402 may also be coupled to a reference voltage, such as an earth.

As described above in relation to Fig. 1 , in some examples the charge determiner 402 is configured to sense current flowing into or out of the battery 408, and to aggregate over time a series of measurements of electric current delivered by and/or to the battery 408 to provide an updated indication of state of charge of the battery 408.

In some examples, such as the example shown in Fig. 3, the battery management system 404 is arranged to be powered by all of the cells of the battery 408. In some examples, the charge determiner 402 is arranged to be powered by all of the cells of the battery 408.

Similar to examples described above in relation to the controller 104 of Fig. 1 , the battery management system 404 may optionally be connected to a communications interface, for example a CAN interface. The battery management system 404 may be configured to wake up from the sleep mode at selected intervals. During waking from the sleep mode, the battery management system 404 may be configured to determine whether to switch to the active mode based on a current measurement obtained from the charge determiner 402. Upon waking from the sleep mode, the battery management system 404 may be configured to check whether any determinations of electric current, and/or Controller Area Network (CAN) messages were generated while the battery management system 404 was in sleep mode. The checking may comprise investigating the contents of a buffer. In some examples, the absence of any determination of electric current or CAN messages causes the battery management system 404 to enter sleep mode.

In some examples the battery management system 404 may be configured to listen to network messages such as CAN messages and/or detect whether current is flowing to/from the battery 408, for example via terminals 410. The battery management system 404 may be configured so that the presence of a determination of electric current or CAN messages causes the battery management system 404 to perform a function, such as update a state of charge value or switch from a sleep mode to an active mode, or vice-versa.

A determination of electric current may be provided by the current determiner 402 broadcasting its measured values. A determination of electric current may be provided by the current determiner 402 writing its measured electric current values to a specific location, and the battery management system 404 reading the values from the specific location. The specific location may be a data store, such as the data store 106 described above. In some examples, a determination of electric current may be provided by the current determiner 402 sending a reading of electric current in response to receiving a request for a reading of electric current sent by the battery management system 404.

The battery management system 404 may be configured to wake up from the sleep mode upon detection that the current determiner is drawing current. In some examples, the battery management system 404 may be configured to wake up from the sleep mode upon detection that a CAN message has been received. In some examples, the battery management system 404 may be configured to wake up from the sleep mode upon detection that a specified amount of time has passed.

The charge determiner 402 may be provided by the charge determiner 102 of Fig. 1 and may, for example, comprise a battery fuel gauge. The battery management system 404 may be configured to switch into the sleep mode in the event that the charge indicator 402 indicates that less than a threshold current has been delivered to or from the battery 408 for a selected interval. In some examples the battery management system 404 is configured to switch into the sleep mode in the event that no CAN messages are received during a selected interval. The battery management system 404 may be configured to switch into the sleep mode in the event that the state of charge of one or more of the cells drops below a selected level.

In some examples, the battery management system 404 may have a further low power mode of operation, such as an ultra-low power mode. The battery management system 404 may be configured to enter such an ultra-low power mode if a second selected condition has been met, for example if a current has not flowed to/from the battery 408 in a second selected time period, for example if the battery module 400 is being stored and has not been used for some time. In such an ultra-low power mode, further components of the battery module 400 may be powered down. For example, a communications interface if present may be powered down, and the battery management system 404 may be configured to periodically power up the communications interface to listen for messages to determine whether it should wake up out of the ultra-low power mode and/or the sleep mode.

It will be appreciated in the context of the present disclosure however that the activities and apparatus outlined herein, such as the operation of the battery module 100 illustrated in Figs. 1 and 2 and described elsewhere in the specification, or the operation of the battery module 400 described in Fig. 3, may be implemented with any kind of logic such as assemblies of logic gates or other kinds of programmable logic such as software and/or computer program instructions executed by a processor. Other kinds of programmable logic also include programmable processors, programmable digital logic (e.g., a field programmable gate array (FPGA), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM)), an application specific integrated circuit, ASIC, or any other kind of digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, such as software and firmware, or any suitable combination thereof.

It will be appreciated that while the description discusses energy storage and in particular electricity storage systems in the form of batteries 108, 408 comprising battery cells, other forms of energy storage apparatus may be used, such as fuel cells or other DC energy storage apparatus. Although Figs. 1 and 3 show a battery 108, 408 comprising three battery cells, of course more or less cells may be used. The controller 104, charge determiner 102 and data store 106 of Fig. 1 may be provided on a single printed circuit board. The battery module 100 may be an enclosure, for example configured to protect components of the battery module 100 such as the battery 108 and/or the controller 104. The terminals 1 10 may be carried by the battery module 100, for example carried by the enclosure, for example on the outside of the enclosure. In some examples, the controller 104 may be provided by a battery management system, BMS. In some examples, the charge determiner 102 comprises a battery fuel gauge.

With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. For example, the controller 104 may be provided as a single integrated microprocessor, or may be provided by a plurality of units. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single functional unit. For example, the data store 106 shown in Fig. 1 may be provided as part of the controller 104. In some examples, the controller 104 of Fig. 1 may be provided by, or provide the functionality of, the battery management system 404 of Fig. 3.

The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. For example the visual indication or display of state of charge described above in relation to Fig. 1 may be used with embodiments described in relation to Fig. 3. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

In some examples, one or more memory elements can store data and/or program instructions used to implement the operations described herein. Embodiments of the disclosure provide tangible, non-volatile, non-transitory storage media comprising program instructions operable to program a processor to perform any one or more of the methods described and/or claimed herein and/or to provide data processing apparatus as described and/or claimed herein.

Claims

A method for providing an indication of state of charge of a battery module, the battery module comprising:

a battery comprising at least one battery cell,

a controller, and

a charge determiner configured to determine the state of charge of the battery based on a characteristic of the at least one battery cell; a determination of the current delivered by or and/or to the battery; and a selected switch-on value and to provide an indication of state of charge to the controller,

the method comprising:

(i) storing an indication of state of charge provided by the charge determiner in the event that the charge determiner is powered down; and

(ii) in the event that the charge determiner is powered up, providing a substitute indication of the state of charge in preference to the state of charge provided by the charge determiner, wherein the substitute state of charge is based on the stored state of charge.

The method of claim 1 , wherein the controller is provided by a battery management system, BMS.

A method according to claim 1 or 2, wherein providing a substitute indication comprises modifying the stored indication based on a change in charge stored in the battery.

The method of claim 3, wherein the change in charge stored in the battery is determined by aggregating over time a series of measurements of electric current delivered by and/or to the battery.

The method of any preceding claim, wherein the controller stores an association between cell voltage and state of charge, and the controller is configured to obtain a cell voltage signal and to use the cell voltage signal and the stored association to determine the substitute indication of state of charge.

6. The method of claim 5 wherein the stored association comprises a look up table.

7. The method of any preceding claim, wherein the substitute indication is provided in preference to the state of charge provided by the charge determiner for a selected number of charge/discharge cycles of the battery.

8. The method of any of claims 1 to 4, wherein the indication of state of charge determined by the charge determiner is based on updating the selected switch on value and an aggregation over time of a series of measurements of electric current delivered by and/or to the battery.

9. The method of claim 8, wherein the charge determiner comprises a data store storing characteristic data defining the charge/discharge characteristics of the battery and the aggregation is based on the characteristic data.

10. The method of claim 9 wherein the characteristic data comprises data relating charging and/or discharging of the battery to at least one of:

chemistry of the battery cells;

battery cell voltage;

state of charge;

rate of charging or discharging; and

a temperature of the battery cells.

1 1. The method of any of claims 7 to 10, wherein the substitute indication is used in preference to the state of charge provided by the charge determiner until a selected condition is met.

12. The method of claim 1 1 , wherein the selected condition is based on comparing the substitute indication and the indication provided by the charge determiner.

13. The method of claim 12, wherein the selected condition comprises the substitute indication and the indication provided by the charge determiner matching to within a selected percentage.

14. The method of claim 1 1 , wherein the selected condition is the receipt of a message from the charge determiner.

15. The method of any preceding claim wherein the charge determiner comprises a battery fuel gauge.

16. A state of charge indicator apparatus configured to provide an indication of state of charge of a battery module, wherein the battery module comprises a battery comprising at least one battery cell, the apparatus comprising:

a charge determiner configured to determine the state of charge of the battery;

a data store; and

a controller arranged to:

obtain an indication of state of charge from the charge determiner;

store the indication in the data store in the event that the charge determiner is powered down; and to

determine a substitute indication of the state of charge based on the stored indication in the event that the charge determiner is powered up.

17. The apparatus of claim 16 wherein the controller is configured to use the substitute indication in preference to the indication provided by the charge determiner.

18. The apparatus of claim 16 or 17 wherein the controller is provided by a battery management system and/or the charge determiner comprises a battery fuel gauge.

19. The apparatus of any of claims 16 to 18 further comprising the at least one battery cell.

20. The apparatus of any of claims 16 to 19 wherein the controller is configured to transmit a network message comprising a unique identifier of the battery module and an indication of the state of charge selected from one of the substitute indication and the indication provided by the charge determiner.

21. An apparatus according to any of claims 16 to 20 configured to perform the method of any of claims 1 to 15.

22. A computer program product comprising program instructions configured to program a programmable processor to perform the method of any of claims 1 to 15.

23. An apparatus for providing an indication of state of charge of a battery comprising a plurality of energy storage cells, the apparatus comprising: a battery management system configured to switch between an active mode in which it operates to balance the cells of the battery and a sleep mode, wherein the sleep mode consumes less power than the active mode; and

a charge determiner for determining a state of charge of the battery;

wherein the apparatus is configured so that, when the battery management system switches to the sleep state, power is maintained in the charge determiner.

24. The apparatus of claim 23, wherein the charge determiner is configured to sense a voltage across a cell of the battery.

25. The apparatus of claim 24 wherein the charge determiner is coupled to sense the voltage by a voltage follower.

26. The apparatus according of any of claims 23 to 25, wherein the charge determiner is configured to sense current flowing into or out of the battery, and to aggregate over time a series of measurements of electric current delivered by and/or to the battery to provide an updated indication of state of charge of the battery.

27. The apparatus according to any of claims 23 to 26, wherein the battery management system is arranged to be powered by all of the cells of the battery.

28. The apparatus according to any of claims 23 to 27, wherein the charge determiner is arranged to be powered by all of the cells of the battery.

29. The apparatus of any of claims 23 to 28, wherein the battery management system is configured to wake up from the sleep mode at selected intervals.

30. The apparatus of claim 29 wherein, during waking from the sleep mode, the battery management system is configured to determine whether to switch to the active mode based on a current measurement obtained from the charge determiner.

31. The apparatus of claim 30 wherein, upon waking from the sleep mode, the battery management system is configured to check whether any determinations of electric current, and/or Controller Area Network (CAN) messages were generated while the battery management system was in sleep mode.

32. The apparatus of claim 31 , wherein the checking comprises investigating the contents of a buffer.

33. The apparatus of claim 31 or 32, wherein the absence of any determination of electric current or CAN messages causes the battery management system to enter sleep mode.

34. The apparatus of any of claims 31 to 33, wherein the presence of a determination of electric current or CAN messages causes the battery management system to update a state of charge value.

35. The apparatus of any of claims 31 to 34, wherein a determination of electric current is provided by the current determiner broadcasting its measured values.

36. The apparatus of any of claims 31 to 34, wherein a determination of electric current is provided by the current determiner writing its measured electric current values to a specific location, and the battery management system reading the values from the specific location.

37. The apparatus of any of claims 31 to 36, wherein a determination of electric current is provided by the current determiner sending a reading of electric current in response to receiving a request for a reading of electric current sent by the battery management system.

38. The apparatus of any of claims 23 to 37 wherein the battery management system is configured to wake up from the sleep mode upon detection that the current determiner is drawing current.

39. The apparatus of any of claims 23 to 38 wherein the battery management system is configured to wake up from the sleep mode upon detection that a CAN message has been received.

40. The apparatus of any of claims 23 to 39 wherein the battery management system is configured to wake up from the sleep mode upon detection that a specified amount of time has passed.

41. The apparatus of any of claims 23 to 40 further comprising the energy storage cells.

42. The apparatus of any of claims 23 to 41 wherein the charge determiner comprises a battery fuel gauge.

43. The apparatus of any of claims 23 to 42 wherein the battery management system is configured to switch into the sleep mode in the event that the charge determiner indicates that less than a threshold current has been delivered to or from the battery for a selected interval.

44. The apparatus of any of claims 23 to 43 wherein the controller is configured to switch into the sleep mode in the event that no CAN messages are received during a specified time period.

45. The apparatus of any of claims 23 to 44 wherein the controller is configured to switch into the sleep mode in the event that the state of charge of one or more of the cells drops below a specified level.

46. An apparatus substantially as described herein with reference to the drawings.