WO2017111907A1

WO2017111907A1 - Passivated battery charging

Info

Publication number: WO2017111907A1
Application number: PCT/US2015/067120
Authority: WO
Inventors: Ketan SODHI; Edgar Hance; David C. VALDEZ
Original assignee: Hewlett Packard Enterprise Development LP
Current assignee: Hewlett Packard Enterprise Development LP
Priority date: 2015-12-21
Filing date: 2015-12-21
Publication date: 2017-06-29
Anticipated expiration: 2018-06-21

Abstract

In one example, a method for charging a battery. It is determined whether the battery is passivated. If the battery is passivated, a recovery charge is performed. The recovery charge includes applying a constant charging current to the battery until a measured voltage of the battery exceeds a limit voltage. The recovery charge further includes applying a pulsed charging current to the battery for a predetermined pulsing time after the measured voltage exceeds the limit voltage.

Description

PASSIVATED BATTERY CHARGING Background

[0001] Many computer systems include a backup battery. This battery may be used, in the event of a system power failure to the computer system, to provide power to certain components of the computer system for a time in order to allow the system to shut down in an orderly way which preserves certain desired data. If the battery is not able to provide sufficient power, for a sufficient time, to those components, this data may be disadvantageously lost. In some cases, the battery may be unable to do so because of passivation.

Brief Description of the Drawings

[0002] FIG. 1 is a schematic block diagram representation of a battery management system in accordance with an example of the present disclosure.

[0003] FIG. 2 is a schematic block diagram representation of another battery management system in accordance with an example of the present disclosure.

[0004] FIG. 3 is a schematic block diagram representation of a

programmable controller usable in the management system of FIG. 2 in accordance with an example of the present disclosure.

[0005] FIG. 4 is a flowchart of a battery management method according to an example of the present disclosure.

[0006] FIG. 5 is a flowchart of a method of charging a battery according to an example of the present disclosure.

[0007] FIG. 6 is a lower-level flowchart of a method of performing a recovery charge usable with the flowchart of FIG. 4 according to an example of the present disclosure.

[0008] FIG. 7 is a schematic block diagram representation of a server that utilizes the battery management of FIG. 1 and/or FIG. 2, and/or the controller of FIG. 3, in accordance with an example of the present disclosure. Detailed Description

[0009] A rechargeable battery which has not been charged in a long time can enter an undercharged, high resistance state. A battery in this state is known as a "passivated" battery; that it, a battery in a deep discharged state. Passivation may occur, for example, when a battery is stored out of a system, unused, for a long period of time. Such a battery may also be included in a system, but in a system which has similarly been unused (i.e. not powered on) for a long period of time.

[0010] Passivation can occur with different types of rechargeable batteries. One such type of battery is a nickel-metal hydride (NiMH) battery. Due to their energy capacity and energy density, NiMH batteries are frequently used as backup batteries in computer systems. A charging circuit in the computer system can recharge the backup battery when it is installed in the computer system. However, passivation may not occur with some types of batteries. For example, lithium-ion batteries go bad over time, but they cannot be revived. Instead, they enter a state of permanent failure once the voltage goes too low as the cells develop an internal short.

[0011] Some backup batteries include multiple battery cells. Each cell may produce a particular nominal voltage, and several cells may be connected in series to form a battery having a higher nominal voltage. In a multiple-cell battery, the individual cells may be depleted at different rates. This depletion imbalance can cause some of the cells to have a higher resistance than others of the cells. Such a multiple-cell battery is considered to be

passivated. When a passivated multiple-cell battery is recharged using a charging circuit which applies a constant current to the battery until the battery reaches a cutoff voltage, the higher resistance can make the battery appear to the charger as if it is fully charged when, in fact, it is not. As such, the charging process can be terminated prematurely, before the battery is fully charged. If a power failure occurs in the computer system, and a passivated backup battery is used to provide power during the shutdown procedure, the battery may not have sufficient energy capacity to provide the appropriate amount of power for the appropriate length of time. As a result, data loss and/or other undesirable effects can result if a passivated battery is used.

[0012] Some batteries, including single-cell batteries, can also appear to be fully charged after a constant current charging process in other situations, and for other reasons.

[0013] As a result, in some examples, a purportedly fully charged battery may be tested after charging by applying a simulated load for a

predetermined time, both of which approximate the use of the battery during power failure. If the battery fails this test, the battery is flagged as defective. While this can prevent data loss from using a battery having insufficient energy capacity, replacing such a battery deemed defective

disadvantageously incurs both expense and time on the part of the computer system owner/operator and/or the manufacturer of the computer and/or battery.

[0014] However, in many cases, a passivated battery, which would likely fail the simulated load test, can be revived to a normal operating condition. By doing this in situ, and automatically, the costs and inconvenience of battery replacement can beneficially be avoided. This significantly improves the function of the computer by ensuring that a battery has sufficient capacity to perform its intended function in a system. And it significantly improves battery performance by reviving (refreshing) the passivated battery to a normal operating condition.

[0015] Referring now to the drawings, there is illustrated an example of a battery management system capable of reviving a passivated battery. The system includes a charging circuit and a programmable controller. In one example, the controller determines whether a battery is passivated and, of so, applies a recovery charge to the battery.

[0016] Considering now a battery management system in greater detail, and with reference to FIG. 1 , a system 100 includes a charging circuit

(charger) 1 10 and a controller 130. The charging circuit 1 10 is connectable to a battery 120. The positive 122 and negative 124 terminals of the battery 120 are connectable to the charging circuit 1 10 and the controller 130.

[0017] The charging circuit 1 10 includes a current source 1 12. The current source 1 12 can be controlled to apply a specified constant current to the battery 120 during charging, recharging, or reviving of the battery 120. The charging circuit 1 10, in some examples, include over voltage protection, over current protection, and/or battery leakage isolation circuits. The charging circuit 1 10 is communicatively coupled to the controller 130 via at least one control line 132. The control line(s) 132 may turn the current source 1 12 on or off, specify the amount of current that is sourced by the current source 1 12, and/or perform other functions.

[0018] The controller 130, which may be a programmable controller, can determine whether the battery 120 is passivated. If the battery 120 is passivated, the controller 130 can control the charging circuit 1 10 to apply a recovery charge to the battery 120. The recovery charge is a charge whose characteristics enable a passivated battery 120 to be revived to the normal operating state, including a nominal energy capacity.

[0019] As is discussed subsequently in greater detail, the recovery charge may be performed by first applying the constant current from the charging circuit 1 10 to the battery 120 until a measured voltage of the battery 120 exceeds a limit voltage, and then by applying a pulsed current to the battery 120 for a predetermined pulsing time after the measured voltage exceeds the limit voltage. In one example, the pulsed current is of same amperage as the constant current. The pulsed current may be generated by turning the current source 1 12 on and off in accordance with certain parameters during the pulsing time. In one example, the pulsed current is generated by alternately turning the charging circuit 1 12 off for a predetermined off time, and then turning the charging circuit 1 12 on until the measured voltage of the battery exceeds the limit voltage. This off and on cycling continues until the predetermined pulsing time is exceeded.

[0020] In examples, some or all of the controller 130 may be implemented in hardware, firmware, software, or a combination of these. [0021] Considering now another battery management system, and with reference to FIG. 2, a system 200 includes a charging circuit 210 with a current source 212, and a controller 230. The charging circuit 210 is connectable to a battery 220. The positive 222 and negative 224 terminals of the battery 220 are connectable to the charging circuit 210 and the controller 230. The charging circuit 210 is communicatively coupled to the controller 230 via at least one control line 232. In some examples, the charging circuit 210, current source 212, battery 220, controller 230, and/or control line(s) 232 are the same as or similar to the charging circuit 1 10, current source 1 12, battery 120, controller 130, and/or control line(s) 132 respectively.

[0022] In some examples, the battery 220 includes multiple battery cells (three cells 226 are illustrated) that are connected in series. In some examples, each cell 226 has a same nominal output voltage, while in other examples, at least two cells 226 have a different nominal output voltage. In some examples, the battery 220 is an NiMH battery and the cells 226 are NiMH cells.

[0023] The system 200 also includes a voltage measuring device 240 that is connectable to the positive 222 and negative 224 terminals of the battery 220. The voltage measuring device 240 may be an A/D converter, a voltmeter, or another type of voltage measuring device 240. The voltage measuring device 240 can be used to controllably measure the output voltage of the battery 220 at various times and under various battery loading conditions. In some examples, the voltage measuring device 240 may be disposed in the controller 230.

[0024] The system 200 further includes a simulated load 250 that can be controllably connected to the battery 220 by the programmable controller 230. The simulated load 250 can be used to test the energy capacity of the battery 220 to determine whether it has sufficient energy capacity for its intended use. In some cases, the simulated load 250 is connected to the battery 220 for a predetermined load time, which in some examples approximates an amount of the time that the battery 220 would be used to power portions of the system 200 during a failure of system power supplied to the system 200. In one example, the battery 220 powers portions of the system to perform a data backup operation during system power failure. The controller 230 can determine, from a voltage of the battery 220 with the simulated load 250 connected to the battery 220, whether the battery 220 is operational (i.e. that it has sufficient energy capacity for its intended use), defective (i.e. that is does not have sufficient energy capacity for its intended use), or should receive a recovery charge and then be re-tested.

[0025] The system 200 also includes a switching circuit 270 to controllably connect the battery 220 to an operational load 280. Where the battery 220 provides backup power during a power failure, the controller 230 detects a failure of system power at a system power input 234, and in response issues a control signal 236 to the switching circuit 270. Upon receipt of the control signal 236, the switching circuit 270 connects the battery 220 to the

operational load 280. As a result, the positive 222 and negative 224 terminals of the battery 220 are connected to the positive 272 and negative 274 inputs of the operational load 280 respectively. The switching circuit 270 may use mechanical switches, electronic switches, or other switching technologies to effect the backup power connection. In some examples, the controller 230 may also disconnect some or all components of the system 200 from system input power to avoid both system power and power from the battery 220 being applied to components of the system 200 at the same time.

[0026] The operational load 280 includes at least a portion of the programmable controller 230, as well as other components. In some examples, these other components include volatile memory 282, non-volatile memory 284, and a memory transfer controller 286. In the event of a power failure, the controller 230 instructs, via signal 238, the memory transfer controller 286 to transfer contents of the volatile memory 282 to the nonvolatile memory 284. In some examples, the transfers occur over a data bus 288 that connects the memories 282, 284, and in some cases also the memory controller 286. This data transfer can preserve the contents of the volatile memory 282 during the power failure so that they can be recovered at a later time, such as for example after system power has been restored to the system 200.

[0027] Considering a programmable controller, and with reference to FIG. 3, a controller 300 includes a processor 310. The controller 300 also includes a memory 320, a power failure detection circuit 330, an A/D (or other voltage measuring device) 340, a simulated load 350, and a load switch 360.

[0028] The power failure detection circuit 330 monitors system power at an input 302. In the event of a system power failure, the power failure detection circuit 330 sends a signal 332 to the processor 310. In response, the processor 310 may generate a signal 312 which is transmitted to a switching circuit which may be external to the controller 300, such as for example backup battery power switching circuit 270 (FIG. 2).

[0029] The A/D 340 has signal inputs 342, 344 that are connected to the position and negative outputs of the battery. The A/D 340 is communicatively coupled to the processor 310 via one or more signals 346. The signals 346 include commands from the processor 310 to the A/D 340 to perform a voltage measurement, and data corresponding to the measured voltage returned from the A/D 340 to the processor 310. The signals 346 may also perform other functions.

[0030] The simulated load 350, in some examples, may be a

programmable load, where at least one signal 352 from the processor 310 specifies at least one characteristic of the load, such as for example the load resistance. The load 350 is connected to, or disconnected from, the battery via the switching circuit 360, which is controlled by the processor 310 via signal 365. When the switching circuit 360 is signaled by the processor via signal 365 to connect the simulated load 350 to the battery, the battery sources current to the simulated load 350 through the lines 352, 354 that are connected to the position and negative outputs of the battery and passed through the switching circuit 360 to the simulated load 350. The load resistance determines the amount of current that is sourced to the load 350 by the battery. In some examples, the simulated load 350 may have a fixed resistance, and the signal 352 may be omitted. By adjusting (or selecting) the load resistance to match or approximate the current drawn when powering an operational load, such as for example operational load 280 (FIG. 2), and by applying the load 350 to the battery for a period of time which corresponds to the period of time which the operational load is to be powered by the battery, an accurate assessment of battery adequacy can be obtained.

[0031] The processor 310 also includes at least one control line 314 to a charging circuit external to the processor 310. The control line(s) 132 may turn the current source 1 12 on or off, specify the amount of current that is sourced by the current source 1 12, and/or perform other functions.

[0032] In some examples, the controller 230 (FIG. 2) may be the controller 300. In other examples, one or more components of the controller 300 may be located external to the controller 300.

[0033] While the lines 312, 314, 332, 346, 352, and 365 are shown as directly connected to the processor 310, in some examples these lines may be connected to the processor 310 indirectly such as through buffers, I/O ports, busses, and/or other intermediary components.

[0034] The memory 320 may be communicatively coupled to the processor 310 via one or more busses 322. Processor-executable instructions of a battery management procedure 324 are stored in or on the memory 320. The battery management procedure 324 includes a charging procedure 325. In operation, the processor 310 accesses the memory 320, retrieves the instructions of the battery management procedure 324, and executes these instructions, including the charging procedure instructions 325 to charge a battery.

[0035] Consider now, with reference to FIG. 4, a flowchart of a

programmable controller of a battery management system. Alternatively, the flowchart of FIG. 4 may be considered as at least a portion of a method implemented in the programmable controller. A method 400 begins when system power is applied. At 404, the battery is charged. The charging process includes testing the battery, and the performance of the charging and testing process 404 is considered a "battery charging cycle". At 406, a failure of system power is awaited. If a failure of system power is detected, then at 408 an operational load is switched over to operate on battery power. Further actions, such as for example a memory data backup operation, may be performed using the operational load.

[0036] Considering now in greater detail the battery charging procedure 404, and with reference to FIG. 5, the battery charging procedure 404 begins at 502 by turning the charger off, and disconnecting all loads from the battery. At 504, the open circuit voltage of the battery is measured. If the measured open circuit voltage is less than a minimum open circuit voltage value (also called the "defective voltage", VDEFECTIVE) ("Yes" branch of 504), then the battery is defective and needs replacement. If the measured open circuit voltage is not less than the defective voltage ("Yes" branch of 504), then at 506 the measured open circuit voltage is compared to a normal or nominal open circuit voltage value (also called the "non-passivated voltage, V_NON- PASSIVATED")- If the measured voltage is not less than the non-passivated voltage ("No" branch of 506), then at 508 the battery is charged via a constant charging current and the battery voltage is periodically measured while charge is being applied until the measured voltage exceeds a cutoff voltage. However, if at 506 the measured voltage is less than the non-passivated voltage ("Yes" branch of 506), then the battery is determined to be passivated and a recovery charge is applied to the battery at 51 0. The recovery charge is explained subsequently in greater detail with reference to FIG. 6.

[0037] After the constant current charge 508 or the recovery charge 51 0 is performed, the method continues at 51 2 by applying a simulated load to the battery and waiting for a predetermined time TV In some examples, the simulated load is chosen to approximate the operational load to be placed on the battery during usage, and the time T corresponds to the length of time that it is desired to have the battery power the operational load. At 51 4 the voltage of the battery is measured while the simulated load is applied. If the measured voltage is greater than a minimum loaded voltage VLOADMIN ("Yes" branch of 51 4), then at 51 6 the simulated load is removed or disconnected from the battery. At 51 8, the battery is charged via a constant charging current for a predetermined time T₂, after which the battery is deemed ready for use.

[0038] However, if the measured voltage at 51 4 is not greater than a minimum loaded voltage VLOADMIN ("NO" branch of 51 4), then at 520 the simulated load is removed or disconnected from the battery. At 522, it is determined whether a prior recovery charge has been performed on the battery during the current battery charging cycle. If the recovery charge 51 0 has been performed ("Yes" branch of 522), then it is concluded that the battery is defective because the prior recovery charge did not revive the battery to proper operation. If the recovery charge 51 0 has not been performed ("No" branch of 522), then the method branches to 51 0 to perform the recovery charge. By providing a recovery charge to a battery that was not determined to be passivated at 506 but which subsequently failed load testing at 51 4, the battery is given a second chance to pass the load test and be denoted as ready for use.

[0039] Considering now in greater detail the recovery charge procedure 51 0, and with reference to FIG. 6, the recovery charge procedure 51 0 begins at 602 by charging the battery via a constant charging current and the battery voltage is periodically measured while charge is being applied until the measured voltage exceeds a limit voltage, V_LIMIT- The limit voltage, in some examples, is the maximum voltage that the charger can support. Then at 604, the battery is charged via a pulsed current for a predetermined time T₃ to complete the recovery charge procedure 51 0.

[0040] In one example, charging the battery via a pulsed current for a predetermined time T₃ at 604 begins, at 606, by turning the charger off and waiting a predetermined time T₄. At 608, after expiration of the

predetermined time T₄, the charger is turned on and the battery is again charged via a constant charging current, and the battery voltage is

periodically measured until the measured voltage exceeds a limit voltage, VLIMIT- Then at 610, it is determined whether the time T₃ has been exceeded. If so ("Yes" branch of 610), the pulsed current charging 604 is complete. If not ("No" branch of 610), then the method branches to 606, and blocks 606 and 608 are repeated.

[0041 ] In the case of a multiple-cell battery having unbalanced cells, the recovery charge allow the cell or cells with the lower voltages to reach full charge. The recovery charge adjusts the battery and decreases the

resistance of the cell or cells through surface reactivation.

[0042] As an example, consider a nominal 4.2V NiMH multi-cell battery having three nominal 1 .4V NiMH battery cells connected in series. For such a battery, in one example, VDEFECTIVE = 2.5 volts, V_NON-PASSIVATED = 3.7 volts, VCUTOFF = 4.3 volts, VLIMIT = 4.4 volts, VLOADMIN = 2.7 volts, T₃ = 15 minutes, and T₄ = 15 milliseconds. Time T corresponds to the amount of time that the operational load is to be powered by the battery. In one example, a 1 .2A simulated load is applied for T = 60 seconds (which corresponds to a battery capacity demand of 20 milliamp-hours). Time T₂ varies according to the time needed to replenish the energy consumed during the load test. These voltage and time parameters are determined by the battery cell characteristics. For example, a battery having a three years warranty may be designed for a seven year life. The battery cells are actually rated at 1 .5V maximum. The batteries are oversized in order to retain enough energy as the cells lose capacity over time. The batteries are then undercharged, in order to increase battery life. In one example, time T₂ = 5 minutes for a constant charging current of 300mA; this corresponds to a slightly higher battery capacity of 25 milliamp-hours, in order to account for tolerances. The value of T₂ depends on the the load size, the duration the load is applied, and the charging current. In this example, the load is 1 .2A for 60 seconds. Battery energy is calculated in milliamp hours (mAh). 0.017 hours = 1 minute and 0.085 Hours = 5 minutes. For the simulated load test, the amount of energy used is calculated as 1 .2A times 0.017 hours = 20mAh. The amount of energy for recharge is calculated as 0.3A times 0.085 hours = 25mAh. Time T4 may vary depending on the battery voltage level. There are three considerations: 1 ) when the battery is being charged, the battery voltage level will appear as a higher closed circuit voltage (CCV); 2) once the charge stops, the battery voltage will settle to the actual battery open-circuit voltage (OCV); and 3) the charger has a hardware limit set by resistors at 4.4V (plus tolerances). The charger will turn off as the CCV level reaches the hardware limit. When the charger turns off, the battery voltage level will begin dropping. At a certain point the charger will turn back on again. During the T₃ = 15 minute pulsed charge, the battery voltage level will slowly increase. As the battery level increases, the charger will turn off more quickly.

[0043] Other battery voltages and/or other battery types may have different values for these various voltage and time parameters.

[0044] Considering now a server that utilizes the battery management system 100 (FIG. 1 ), 200 (FIG. 2), and/or the controller 300 (FIG. 3), and with reference to FIG. 7, a server 700 includes at least one processor 710 coupled to at least one main memory 720. In some examples, each processor 710 is coupled to a different main memory 720, while in other examples the main memory 720 can be shared among processors 710. The processors 710 are connected to at least one bus 705. Where the server 700 includes multiple busses 705, various ones of the busses 705 may be interconnected via various interfaces (not shown). While the memory 720 is illustrated as being directly coupled to the processor 710, in other examples the memory 720 may be coupled to the bus 705.

[0045] At least one I/O interface 730 is coupled to the bus 705. There may be many I/O interface 730 of many types such as, for example, video, USB, ACPI, keyboard, mouse, and network interfaces. In some examples, at least some of these interfaces 730 are implemented as PCIe devices.

[0046] A disk array (DA) controller 740 is coupled to the bus 705. At least one hard disk drive 745 is coupled to the disk array controller 740. The number of hard drives can vary depending on the user's criteria, space needed, and desired level of redundancy (e.g. RAID mode). The disk array controller 740 acts as an interface between the various components of the server, such as for example the processor(s) 710, memory 720, I/O

interface(s) 730, etc., and the hard drive(s) 745. In operation, one or more of these components send data to the disk array controller 740, which in turn manages how, when, and where the data is stored on the drive(s) 745. In some examples, the disk array controller 740 also monitors the status and health of the drive(s) 745. As such, the disk array controller 740 may be considered a "smart" controller.

[0047] The disk array controller 740 includes a DA engine 750 which orchestrates the operation of the disk array controller 740. The DA engine 750 implements the RAID functionality, monitors the drive(s) 745, and tracks where the data it receives for storage is located. The DA engine 750 is coupled to a DA ROM 760 which in some examples is, or includes, a reprogrammable ROM. The DA ROM 760 contains DA firmware 762 which may implement some or all of the functionality of the DA engine 750. The DA engine 750, in one example, is a "RAID on a chip" ASIC which implements an XOR engine to provide the RAID functionality. The DA engine 750 also implements a memory transfer controller 755 to transfer data between a volatile memory 776 and a non-volatile memory 778. In some examples, the memory transfer controller 755 is the memory transfer controller 286 (FIG. 2); the volatile memory 776 is the volatile memory 282 (FIG. 2); and the nonvolatile memory 778 is the non-volatile memory 284 (FIG. 2).

[0048] The volatile memory 776 and non-volatile memory 778 are part of a cache module 770. The cache module 770 functions as an array accelerator. Since data transfer operations to and from some types of hard drive(s) 745 may be slow, the cache module 770 is used to speed up the process by providing read-ahead caching and write-back caching. During a write operation, the disk array controller 740 can temporarily store data in the cache module 770 while it waits for the hard drive(s) 745 to become available to receive and store additional data.

[0049] The disk array controller 740 provides indefinite write cache data retention in the case of an unexpected system power failure. Once data to be written to the hard drive(s) 745 has been received by the disk array controller 745 and stored to the volatile memory 776, the disk array controller 740 reports to the system that the data has been saved to the hard drive(s) 745 in order to accelerate system performance, even though the write data has not yet been sent to the hard drive(s) 745. Thus if power is removed from the volatile memory 776 due to a system power failure, its data contents would be lost , and never sent to the hard drive(s) 745. To avoid this, upon detection of system power failure, the memory transfer controller 755 saves the contents of the volatile memory 776 in the non-volatile memory 778, from where they can be subsequently restored and sent to the hard drive(s) 745 when system power is restored.

[0050] A backup battery 785 provides the power to the pertinent

components of the disk array controller 740 to perform this data save operation upon system power failure. The battery 785, in some examples, is the battery 120 (FIG. 1 ) or 220 (FIG. 2). The cache module 770 includes a battery management controller 780 which conditions the battery 785 using a battery charger 772, detects a failure of system power 775, and switches to battery power via battery switch 774. In some examples, the battery management controller 780 is the controller 130 (FIG. 1 ), 230 (FIG. 2), or 300 (FIG. 3). In some examples, the battery 785 is the battery 220 (FIG. 2) or 120 (FIG. 1 ). In some examples, the battery charger 772 is the battery charging circuit 210 (FIG. 2) or 1 10 (FIG. 1 ). In some examples, the battery switch 774 is the battery backup power switch 270 (FIG. 2).

[0051] The battery management controller 780 includes a memory 782, which in some examples is, or includes, a reprogrammable ROM. The memory 782 may be the memory 320 (FIG. 3). Battery management firmware 784 which the controller 780 uses to implement its functionality is stored in the memory 782. The battery management firmware 784 may be, or include, the battery management procedure 324 (FIG. 3).

[0052] From time to time the DA firmware 762 and/or the battery

management firmware 784 may be updated via a firmware payload 790. In one example, the firmware payload 790 may be received electronically at an I/O interface 730 of the server 700, such as a network interface. In one example, the firmware payload 790 is a DA firmware update payload which includes a battery management firmware update payload. The DA firmware update is installed in the DA ROM 760 as the DA firmware 762. The DA firmware 762 includes a battery management controller firmware update procedure 764, and a battery management firmware payload 766. When the battery management controller firmware update procedure 764 is executed, a check is performed to determine whether the version of the battery

management firmware 784 that is presently installed in the battery

management controller 780 is older than the version of the battery

management firmware payload 766. If so, the battery management controller firmware update procedure 764 installs the battery management firmware payload 766 in the memory 782 as the battery management firmware 784.

[0053] From the foregoing it will be appreciated that the systems and methods provided by the present disclosure represent a significant advance in the art. Although several specific examples have been described and illustrated, the disclosure is not limited to the specific methods, forms, or arrangements of parts so described and illustrated. For example, examples of the disclosure are not limited to NiMH batteries. This description should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing examples are illustrative, and different features or elements may be included in various combinations that may be claimed in this or a later application. Unless otherwise specified, operations of a method claim need not be performed in the order specified. Similarly, blocks in diagrams or numbers (such as (1 ), (2), etc.) should not be construed as operations that proceed in a particular order. Additional blocks/operations may be added, some blocks/operations removed, or the order of the blocks/operations altered and still be within the scope of the disclosed examples. Further, methods or operations discussed within different figures can be added to or exchanged with methods or operations in other figures. Further yet, specific numerical data values (such as specific quantities, numbers, categories, etc.) or other specific information should be interpreted as illustrative for discussing the examples. Such specific information is not provided to limit examples. The disclosure is not limited to the above-described implementations, but instead is defined by the appended claims in light of their full scope of equivalents. Where the claims recite "a" or "a first" element of the equivalent thereof, such claims should be understood to include incorporation of at least one such element, neither requiring nor excluding two or more such elements. Where the claims recite "having", the term should be understood to mean

"comprising".

Claims

What is claimed is:

1 . A method for charging a battery, comprising:

determining whether the battery is passivated; and

if the battery is passivated, performing a recovery charge by

applying a constant charging current to the battery until a measured voltage of the battery exceeds a limit voltage, and

applying a pulsed charging current to the battery for a predetermined pulsing time after the measured voltage exceeds the limit voltage.

2. The method of claim 1 , wherein applying the pulsed charging current comprises:

removing the constant charging current from the battery for a

predetermined off time;

after the off time, reapplying the pulsed charging current to the battery until the measured voltage of the battery exceeds the limit voltage; and

repeating the removing and reapplying for the predetermined pulsing time.

3. The method of claim 1 , wherein the determining comprises:

measuring an open circuit voltage of the battery; and

determining that the battery is passivated if the open circuit voltage is greater than a predetermined defective voltage and less than a

predetermined non-passivated voltage.

4. The method of claim 3, wherein the open circuit voltage is greater than the predetermined non-passivated voltage, comprising:

applying the constant charging current to the battery until the

measured voltage of the battery exceeds a cutoff voltage,

connecting a predetermined electrical load to the battery for a predetermined load time, measuring a loaded voltage of the battery after the predetermined load time, and

if the loaded voltage is greater than or equal to a predetermined minimum loaded voltage, applying a constant charging current to the battery for a predetermined recharging time.

5. The method of claim 5, wherein the loaded voltage is less than a predetermined minimum loaded voltage, comprising:

performing the recovery charge if no recovery charge has been applied to the battery during a current battery charging cycle; and

identifying the battery as defective if a previous recovery charge has been applied to the battery during the current battery charging cycle.

6. The method of claim 1 , wherein the battery is a NiMH battery comprising multiple NiMH cells.

7. The method of claim 6, wherein at least one cell of a passivated NiMH battery has a higher resistance than at least one other cell of the battery.

8. A battery management system, comprising:

a charging circuit connectable to a battery to controllably apply a constant current to the battery; and

a programmable controller, coupled to the charging circuit and the battery, to determine whether the battery is passivated and, if the battery is passivated, to control the charging circuit to apply a recovery charge to the battery by applying the constant current to the battery until a measured voltage of the battery exceeds a limit voltage, and by applying a pulsed current to the battery for a predetermined pulsing time after the measured voltage exceeds the limit voltage.

9. The system of claim 8, wherein the programmable controller applies the pulsed current by alternately turning off the charging circuit for a predetermined off time, and turning on the charging circuit until the measured voltage of the battery exceeds the limit voltage, until the predetermined pulsing time is exceeded.

10. The system of claim 8, comprising:

a simulated load controllably connected to the battery by the

programmable controller for a predetermined load time; the controller further to determine, from a voltage of the battery with the simulated load connected, whether the battery is operational or defective.

1 1 . The system of claim 8, comprising:

a switching circuit to controllably connect the battery to an operational load when a system power failure is detected.

12. The system of claim 1 1 , wherein the operational load comprises the programmable controller, volatile memory, non-volatile memory, and a memory transfer controller, and wherein the memory transfer controller transfers contents of the volatile memory to a non-volatile memory during the power failure.

13. A non-transitory computer-readable storage medium having an executable program stored thereon, wherein the program instructs a processor to:

measure an open circuit voltage to determine that a battery is passivated;

control a charger circuit to apply a constant charging current to the passivated battery until a measured voltage of the battery exceeds a limit voltage; and control the charger circuit to apply a pulsed charging current to the passivated battery for a predetermined pulsing time after the measured voltage exceeds the limit voltage.

14. The medium of claim 13, wherein to apply the pulsed charging current the program further instructs the processor to alternately, until the predetermined pulsing time is exceeded:

turn the charging circuit off for a predetermined off time; and control the charger circuit to reapply the pulsed charging current to the battery until the measured voltage of the battery exceeds the limit voltage.

15. The medium of claim 13, wherein the program further instructs the processor to:

connect a predetermined electrical load to the battery for a

predetermined load time;

measure a loaded voltage of the battery after the predetermined load time; and

if the loaded voltage is greater than or equal to a predetermined minimum loaded voltage, apply a constant charging current to the battery for a predetermined recharging time to recharge the battery.