Electronic battery tester configured to predict a load test result based on open circuit voltage, temperature, cranking size rating, and a dynamic parameter

[0001] The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/408,542, filed Sep. 5, 2002, the content of which is hereby incorporated by reference in its entirety.

[0002] The present invention relates to testing storage batteries. More specifically, the present invention relates to predicting a high-rate load test result for a storage battery by using a dynamic parameter testing technique such as a conductance testing technique.

[0003] Storage batteries, such as lead acid storage batteries of the SLI (Starting, lighting and ignition) type used in the automotive industry, have existed for many years. However, understanding the nature of such storage batteries, how such storage batteries operate and how to accurately test such batteries has been an ongoing endeavor and has proved quite difficult.

[0004] There has been a long history of attempts to accurately test the condition of storage batteries for starting and other high-rate applications. A standard technique for testing a battery is referred as the Adjustable Load Test. This test is conducted on a charged battery according to the Battery Service Manual of the Battery Council International:

• [0005] 1) Measure the temperature of a center cell. Cover battery with a damp cloth.
• [0006] 2) Connect a voltmeter and load test leads to the appropriate battery terminals. Be sure the terminals are free of corrosion.
• [0007] 3) Apply a test load equivalent to 50% of the Cold Cranking Ampere Performance (CCA) at 0° F. rating of the battery for 15 seconds.
• [0008] 4) Read and record the voltage at 15 seconds; remove the load.
• [0009] 5) Determine the minimum passing voltage based on the battery's test temperature:

[0010]

a)	70° F. and above:	9.6 V
b)	60° F.	9.5 V
c)	50° F.	9.4 V
d)	40° F.	9.3 V
e)	30° F.	9.1 V
f)	20° F.	8.9 V
g)	10° F.	8.7 V
h)	0° F.	8.5 V

• [0011] 6) If the test voltage is above the minimum, return the battery to service.
• [0012] 7) If test voltage is below the minimum and the stable battery open circuit voltage is above 12.4 volts (75% state of charge), the battery should be replaced.
• [0013] 8) If test voltage is below the minimum and the stable battery open circuit voltage is below 12.4 volts, the battery should be charged and the load test repeated. If the battery fails again, it should be replaced.

[0014] Although the load test provides data that is useful for determining the condition of a battery that has been in service, it has certain drawbacks. First, the load test requires that the battery be sufficiently, and preferably fully, charged in order that it can supply the battery's maximum power to the load. Second, the battery becomes somewhat depleted as a result of the test discharge and therefore leaves it in a less than ideal condition. Third, the standard load test equipment is quite heavy and bulky to handle heavy current loads and as such is not very portable. Fourth, sparks may be produced during the load test. Fifth, the load test takes a finite time to discharge the battery and the equipment must often be cooled between tests to prevent overheating. Sixth, the battery is often at a temperature that departs from ambient testing conditions (70° F.) and as such operators are not always aware of the correct comparison voltage to determine if the battery should be replaced. Typically, operators remember the 70° F. value of 9.6 volts only. Therefore, it is desirable to obtain such load test voltage data by using a more amenable testing technique than the method described above.

[0015] More recently, techniques have been pioneered by Dr. Keith S. Champlin and Midtronics, Inc. for testing storage batteries by measuring the conductance and other properties of the batteries. Aspects of these techniques are described in a number of United States patents, for example, U.S. Pat. No. 3,873,911, issued Mar. 25, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,816,768, issued Mar. 28, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE; U.S. Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING; U.S. Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH AUTOMATIC VOLTAGE SCALING TO DETERMINE DYNAMIC CONDUCTANCE; U.S. Pat. No. 4,912,416, issued Mar. 27, 1990, to Champlin, entitled ELECTRONIC BATTERY TESTING DEVICE WITH STATE-OF-CHARGE COMPENSATION; U.S. Pat. No. 5,140,269, issued Aug. 18, 1992, to Champlin, entitled ELECTRONIC TESTER FOR ASSESSING BATTERY/CELL CAPACITY; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994, entitled METHOD AND APPARATUS FOR SUPPRESSING TIME VARYING SIGNALS IN BATTERIES UNDERGOING CHARGING OR DISCHARGING; U.S. Pat. No. 5,572,136, issued Nov. 5, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,574,355, issued Nov. 12, 1996, entitled METHOD AND APPARATUS FOR DETECTION AND CONTROL OF THERMAL RUNAWAY IN A BATTERY UNDER CHARGE; U.S. Pat. No. 5,585,416, issued Dec. 10, 1996, entitled APPARATUS AND METHOD FOR STEP-CHARGING BATTERIES TO OPTIMIZE CHARGE ACCEPTANCE; U.S. Pat. No. 5,585,728, issued Dec. 17, 1996, entitled ELECTRONIC BATTERY TESTER WITH AUTOMATIC COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,589,757, issued Dec. 31, 1996, entitled APPARATUS AND METHOD FOR STEP-CHARGING BATTERIES TO OPTIMIZE CHARGE ACCEPTANCE; U.S. Pat. No. 5,592,093, issued Jan. 7, 1997, entitled ELECTRONIC BATTERY TESTING DEVICE LOOSE TERMINAL CONNECTION DETECTION VIA A COMPARISON CIRCUIT; U.S. Pat. No. 5,598,098, issued Jan. 28, 1997, entitled ELECTRONIC BATTERY TESTER WITH VERY HIGH NOISE IMMUNITY; U.S. Pat. No. 5,656,920, issued Aug. 12, 1997, entitled METHOD FOR OPTIMIZING THE CHARGING LEAD-ACID BATTERIES AND AN INTERACTIVE CHARGER; U.S. Pat. No. 5,757,192, issued May 26, 1998, entitled METHOD AND APPARATUS FOR DETECTING A BAD CELL IN A STORAGE BATTERY; U.S. Pat. No. 5,821,756, issued Oct. 13, 1998, entitled ELECTRONIC BATTERY TESTER WITH TAILORED COMPENSATION FOR LOW STATE-OF-CHARGE; U.S. Pat. No. 5,831,435, issued Nov. 3, 1998, entitled BATTERY TESTER FOR JIS STANDARD; U.S. Pat. No. 5,914,605, issued Jun. 22, 1999, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. 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No. 6,259,254, issued Jul. 10, 2001, entitled APPARATUS AND METHOD FOR CARRYING OUT DIAGNOSTIC TESTS ON BATTERIES AND FOR RAPIDLY CHARGING BATTERIES; U.S. Pat. No. 6,262,563, issued Jul. 17, 2001, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX ADMITTANCE OF CELLS AND BATTERIES; U.S. Pat. No. 6,294,896, issued Sep. 25, 2001; entitled METHOD AND APPARATUS FOR MEASURING COMPLEX SELF-IMMITANCE OF A GENERAL ELECTRICAL ELEMENT; U.S. Pat. No. 6,294,897, issued Sep. 25, 2001, entitled METHOD AND APPARATUS FOR ELECTRONICALLY EVALUATING THE INTERNAL TEMPERATURE OF AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,304,087, issued Oct. 16, 2001, entitled APPARATUS FOR CALIBRATING ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,310,481, issued Oct. 30, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,313,607, issued Nov. 6, 2001, entitled METHOD AND APPARATUS FOR EVALUATING STORED CHARGE IN AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,313,608, issued Nov. 6, 2001, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,316,914, issued Nov. 13, 2001, entitled TESTING PARALLEL STRINGS OF STORAGE BATTERIES; U.S. Pat. No. 6,323,650, issued Nov. 27, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,329,793, issued Dec. 11, 2001, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,331,762, issued Dec. 18, 2001, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Pat. No. 6,332,113, issued Dec. 18, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,351,102, issued Feb. 26, 2002, entitled AUTOMOTIVE BATTERY CHARGING SYSTEM TESTER; U.S. Pat. No. 6,359,441, issued Mar. 19, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,363,303, issued Mar. 26, 2002, entitled ALTERNATOR DIAGNOSTIC SYSTEM, U.S. Pat. No. 6,392,414, issued May 21, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,417,669, issued Jul. 9, 2002, entitled SUPPRESSING INTERFERENCE IN AC MEASUREMENTS OF CELLS, BATTERIES AND OTHER ELECTRICAL ELEMENTS; U.S. Pat. No. 6,424,158, issued Jul. 23, 2002, entitled APPARATUS AND METHOD FOR CARRYING OUT DIAGNOSTIC TESTS ON BATTERIES AND FOR RAPIDLY CHARGING BATTERIES; U.S. Pat. No. 6,441,585, issued Aug. 17, 2002, entitled APPARATUS AND METHOD FOR TESTING RECHARGEABLE ENERGY STORAGE BATTERIES; U.S. Pat. No. 6,445,158, issued Sep. 3, 2002, entitled VEHICLE ELECTRICAL SYSTEM TESTER WITH ENCODED OUTPUT; U.S. Pat. No. 6,456,045, issued Sep. 24, 2002, entitled INTEGRATED CONDUCTANCE AND LOAD TEST BASED ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,466,025, issued Oct. 15, 2002, entitled ALTERNATOR TESTER; U.S. Pat. No. 6,466,026, issued Oct. 15, 2002, entitled PROGRAMMABLE CURRENT EXCITER FOR MEASURING AC IMMITTANCE OF CELLS AND BATTERIES; U.S. Ser. No. 09/703,270, filed Oct. 31, 2000, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/780,146, filed Feb. 9, 2001, entitled STORAGE BATTERY WITH INTEGRAL BATTERY TESTER; U.S. Ser. No. 09/816,768, filed Mar. 23, 2001, entitled MODULAR BATTERY TESTER; U.S. Ser. No. 09/756,638, filed Jan. 8, 2001, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Ser. No. 09/862,783, filed May 21, 2001, entitled METHOD AND APPARATUS FOR TESTING CELLS AND BATTERIES EMBEDDED IN SERIES/PARALLEL SYSTEMS; U.S. Ser. No. 09/960,117, filed Sep. 20, 2001, entitled IN-VEHICLE BATTERY MONITOR; U.S. Ser. No. 09/908,389, filed Jul. 18, 2001, entitled BATTERY CLAMP WITH INTEGRATED CIRCUIT SENSOR; U.S. Ser. No. 09/908,278, filed Jul. 18, 2001, entitled BATTERY CLAMP WITH EMBEDDED ENVIRONMENT SENSOR; U.S. Ser. No. 09/880,473, filed Jun. 13, 2001; entitled BATTERY TEST MODULE; U.S. Ser. No. 09/940,684, filed Aug. 27, 2001, entitled METHOD AND APPARATUS FOR EVALUATING STORED CHARGE IN AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Ser. No. 60/330,441, filed Oct. 17, 2001, entitled ELECTRONIC BATTERY TESTER WITH RELATIVE TEST OUTPUT; U.S. Ser. No. 60/348,479, filed Oct. 29, 2001, entitled CONCEPT FOR TESTING HIGH POWER VRLA BATTERIES; U.S. Ser. No. 10/046,659, filed Oct. 29, 2001, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Ser. No. 09/993,468, filed Nov. 14, 2001, entitled KELVIN CONNECTOR FOR A BATTERY POST; U.S. Ser. No. 09/992,350, filed Nov. 26, 2001, entitled ELECTRONIC BATTERY TESTER, U.S. Ser. No. 60/341,902, filed Dec. 19, 2001, entitled BATTERY TESTER MODULE; U.S. Ser. No. 10/042,451, filed Jan. 8, 2002, entitled BATTERY CHARGE CONTROL DEVICE, U.S. Ser. No. 10/073,378, filed Feb. 8, 2002, entitled METHOD AND APPARATUS USING A CIRCUIT MODEL TO EVALUATE CELL/BATTERY PARAMETERS; U.S. Ser. No. 10/093,853, filed Mar. 7, 2002, entitled ELECTRONIC BATTERY TESTER WITH NETWORK COMMUNICATION; U.S. Ser. No. 60/364,656, filed Mar. 14, 2002, entitled ELECTRONIC BATTERY TESTER WITH LOW TEMPERATURE RATING DETERMINATION; U.S. Ser. No. 10/098,741, filed Mar. 14, 2002, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Ser. No. 10/101,543, filed Mar. 19, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/112,114, filed Mar. 28, 2002; U.S. Ser. No. 10/109,734, filed Mar. 28, 2002; U.S. Ser. No. 10/112,105, filed Mar. 28, 2002, entitled CHARGE CONTROL SYSTEM FOR A VEHICLE BATTERY; U.S. Ser. No. 10/112,998, filed Mar. 29, 2002, entitled BATTERY TESTER WITH BATTERY REPLACEMENT OUTPUT; U.S. Ser. No. 10/119,297, filed Apr. 9, 2002, entitled METHOD AND APPARATUS FOR TESTING CELLS AND BATTERIES EMBEDDED IN SERIES/PARALLEL SYSTEMS; U.S. Ser. No. 10/128,790, filed Apr. 22, 2002, entitled METHOD OF DISTRIBUTING JUMP-START BOOSTER PACKS; U.S. Ser. No. 60/379,281, filed May 8, 2002, entitled METHOD FOR DETERMINING BATTERY STATE OF CHARGE; U.S. Ser. No. 10/143,307, filed May 10, 2002, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 60/387,046, filed Jun. 7, 2002, entitled METHOD AND APPARATUS FOR INCREASING THE LIFE OF A STORAGE BATTERY; U.S. Ser. No. 10/177,635, filed Jun. 21, 2002, entitled BATTERY CHARGER WITH BOOSTER PACK; U.S. Ser. No. 10/207,495, filed Jul. 29, 2002, entitled KELVIN CLAMP FOR ELECTRICALLY COUPLING TO A BATTERY CONTACT; U.S. Ser. No. 10/200,041, filed Jul. 19, 2002, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE; U.S. Ser. No. 10/217,913, filed Aug. 13, 2002, entitled, BATTERY TEST MODULE; U.S. Ser. No. 60/408,542, filed Sep. 5, 2002, entitled BATTERY TEST OUTPUTS ADJUSTED BASED UPON TEMPERATURE; U.S. Ser. No. 10/246,439, filed Sep. 18, 2002, entitled BATTERY TESTER UPGRADE USING SOFTWARE KEY; U.S. Ser. No. 60/415,399, filed Oct. 2, 2002, entitled QUERY BASED ELECTRONIC BATTERY TESTER; and U.S. Ser. No. 10/263,473, filed Oct. 2, 2002, entitled ELECTRONIC BATTERY TESTER WITH RELATIVE TEST OUTPUT; U.S. Ser. No. 60/415,796, filed Oct. 3, 2002, entitled QUERY BASED ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/271,342, filed Oct. 15, 2002, entitled IN VEHICLE BATTERY MONITOR; U.S. Ser. No. 10/270,777, filed Oct. 15, 2002, entitled PROGRAMMABLE CURRENT EXCITER FOR MEASURING AC IMMITTANCE OF CELLS AND BATTERIES; U.S. Ser. No. 10/310,515, filed Dec. 5, 2002, entitled BATTERY TEST MODULE; U.S. Ser. No. 10/310,490, filed Dec. 5, 2002, entitled BATTERY TEST MODULE; U.S. Ser. No. 10/310,385 entitled ELECTRONIC BATTERY TESTER, U.S. Ser. No. 60/437,255, filed Dec. 31, 2002, entitled REMAINING TIME PREDICTIONS, U.S. Ser. No. 60/437,224, filed Dec. 31, 2002, entitled DISCHARGE VOLTAGE PREDICTIONS, U.S. Ser. No. 60/437,611, entitled REMAINING TIME PREDICTIONS, which are incorporated herein in their entirety.

[0016] In general, battery testers, which determine the condition of the battery as a function of measured dynamic conductance of the battery, carry out the conductance measurement by injecting or drawing a small AC current (less than about 2 amperes) through the battery and measuring the resulting AC voltage. Since this technique only involves the use of a small AC current to determine conductance, it is easy to perform, does not discharge the battery, is relatively rapid and is free from sparking.

[0017] The present invention is directed to the use of a dynamic battery parameter, coupled with battery voltage, temperature and Cold Cranking Performance rating (CCA), to determine how a battery would perform under an actual load test. A method and apparatus for testing a storage battery is provided in which a battery is measured to obtain a battery dynamic parameter value such as conductance. The battery is measured to obtain a stable open circuit voltage and a battery temperature value. The load test voltage of the battery is estimated as a function of the battery dynamic parameter value, the open circuit voltage value, the battery temperature value and the battery CCA rating. This voltage value is compared to the minimum requirements for the battery listed above and an output indicative of a condition of the battery is provided.

[0021] The present invention provides a method and apparatus for predicting how a battery would perform under a load test by employing a dynamic parameter testing technique. Although the example embodiments of the present invention described below relate to estimating load test values from battery conductance measurements, dynamic parameters other than battery conductance may be utilized without departing from the spirit and scope of the invention. Examples of other dynamic parameters include dynamic resistance, admittance, impedance, reactance, susceptance or their combinations.

[0022] FIG. 1 is a simplified block diagram of battery test circuitry 16 in accordance with an embodiment of the present invention. Apparatus 16 is shown coupled to battery 12, which includes a positive battery terminal 22 and a negative battery terminal 24. Battery 12 has a CCA rating and a load test voltage rating.

[0023] In preferred embodiments, circuitry 16 operates, with the exceptions and additions as discussed below, in accordance with battery testing methods described in one or more of the United States patents obtained by Dr. Champlin and Midtronics, Inc. and listed above. Circuitry 16 operates in accordance with one embodiment of the present invention and determines the conductance (G) of battery 12 and the open circuit voltage (OCV) between terminals 22 and 24 of battery 12. Circuitry 16 includes current source 50, differential amplifier 52, analog-to-digital converter 54 and microprocessor 56. Amplifier 52 is capacitively coupled to battery 12 through capacitors C₁ and C₂. Amplifier 52 has an output connected to an input of analog-to-digital converter 54. Microprocessor 56 is connected to system clock 58, memory 60, memory 62 and analog-to-digital converter 54. Microprocessor 56 is also capable of receiving an input from input devices 66 and 68. Microprocessor 56 also connects to output device 72.

[0024] In operation, current source 50 is controlled by microprocessor 56 and provides a current I in the direction shown by the arrow in FIG. 1. In one embodiment, this is a square wave or a pulse. Differential amplifier 52 is connected to terminals 22 and 24 of battery 12 through capacitors C₁ and C₂, respectively, and provides an output related to the voltage potential difference between terminals 22 and 24. In a preferred embodiment, amplifier 52 has a high input impedance. Circuitry 16 includes differential amplifier 70 having inverting and noninverting inputs connected to terminals 24 and 22, respectively. Amplifier 70 is connected to measure the OCV of battery 12 between terminals 22 and 24. The output of amplifier 70 is provided to analog-to-digital converter 54 such that the voltage across terminals 22 and 24 can be measured by microprocessor 56.

[0025] Circuitry 16 is connected to battery 12 through a four-point connection technique known as a Kelvin connection. This Kelvin connection allows current I to be injected into battery 12 through a first pair of terminals while the voltage V across the terminals 22 and 24 is measured by a second pair of connections. Because very little current flows through amplifier 52, the voltage drop across the inputs to amplifier 52 is substantially identical to the voltage drop across terminals 22 and 24 of battery 12. The output of differential amplifier 52 is converted to a digital format and is provided to microprocessor 56. Microprocessor 56 operates at a frequency determined by system clock 58 and in accordance with programming instructions stored in memory 60.

[0026] Microprocessor 56 determines the conductance of battery 12 by applying a current pulse I using current source 50. The microprocessor determines the change in battery voltage due to the current pulse I using amplifier 52 and analog-to-digital converter 54. The value of current I generated by current source 50 is known and is stored in memory 60. Microprocessor 56 calculates the conductance of battery 12 using the following equation:

[0027] $\begin{array}{cc}\mathrm{Conductance}=G=\frac{\Delta I}{\Delta V}& \mathrm{Equation}1\end{array}$
where ΔI is the change in current flowing through battery 12 due to current source 50 and ΔV is the change in battery voltage due to applied current ΔI. In some embodiments circuitry 16 also includes a temperature sensor 74, coupled to microprocessor 56, that can be thermally coupled to battery 12 to thereby measure a temperature of battery 12 and provide the measured battery temperature value(s) to microprocessor 56. In the preferred embodiment, the battery temperature would be measured using an infrared signal from the outside of the battery. In other embodiments, instead of being measured, the temperature of battery 12 may be estimated or input by a tester user through input 66, for example. Microprocessor 56 can also use other information input from input device 66 provided by, for example, an operator. This information may consist of the particular type of battery, location, time, the name of the operator, the CCA rating of the battery, the rated load test voltage of the battery, etc.

[0028] Under the control of microprocessor 56, battery tester 16 estimates a load test voltage of battery 12 as a function of the battery conductance G, the OCV, the battery temperature and the CCA rating of battery 12. Further, battery tester 16 compares the estimated load test voltage with the rated load test voltage of battery 12 and outputs the state of health of battery 12 based on this comparison. Details regarding the derivation of an algorithm utilized by battery tester 16 to estimate the load test voltage of battery 12 are provided below. The algorithm included below was derived by taking a representative sample of batteries of different sizes and ages and testing them for their conductance and reactions to various loads at various temperatures.

[0029] It was found that battery conductance varied with temperature in a substantially predictable curvilinear manner. At cold temperatures it would drop rapidly, while at high temperatures it was higher and more constant. This occurs primarily as a result of the variation of the resistance of the electrolyte with temperature. It was found that the specific conductance could be fitted to a third order polynomial equation with temperature. Using the given temperature of the battery, the conductance at any other temperature can then be predicted by multiplying and dividing by the appropriate temperature factors obtained from this temperature curve.

[0030] With fully charged batteries of a given conductance, it is found that the instantaneous loaded voltage is dependent on a voltage that is less than the OCV of the battery. This activation voltage is temperature dependent and can be linearly related:
V=V_act−I*R
or
V=V_act−I/G  (Equation 2)
where V is an instantaneous voltage, V_act is the temperature related fully charged activation voltage, I is the discharge current, R is the battery resistance and G is the battery conductance.

[0031] Because batteries are not always at full charge and at a standard temperature (temperature defined in a battery test standard), properties of the battery in a fully charged condition at a standard temperature need be estimated. It was found that using the initial voltage or OCV as a measure of the discharge of the battery and also using the temperature of the battery, the conductance could be compensated for by a mathematical relationship to predict that of a fully charged battery under standard conditions. For example, conductance can be expressed as:
Gcomp=G*f1(T,OCV)  Equation 3
G₇₀=Gcomp*f2(70)/f2(T)  Equation 4
where Gcomp is conductance compensated to full charge at the OCV and temperature of the battery, G₇₀ is conductance at full charge and 70° F., f1(T,OCV) is a function to compensate the conductance at a given temperature and voltage, and f2(T) is a function of the specific conductance at a given temperature.

[0032] Since the conductance can be corrected mathematically to full charge, the need to recharge moderately discharged batteries before testing or warming or cooling the battery to test conditions is eliminated.

[0033] Thus, knowing the temperature and the conductance (compensated mathematically to full charge) the initial voltage under load can be estimated. V_act is easily calculated for various temperatures by measuring the conductance or the resistance of the fully charged battery and then running the discharge for a short time (2 seconds, for example). Using Equation 2, V_act can be calculated by adding the I*R (or I/G) value to the initial voltage where I is half the CCA rating. By comparing many temperatures and battery types, it is found that V_act varies approximately linearly with temperature and therefore can be predicted using temperature alone.
V_act=k1*T+k2  Equation 5
where T is the battery temperature and k1 and k2 are constants.

[0034] Thus the instantaneous load test value at a standard test temperature (70° F.) can be predicted using the combined equations:
V_init70=70*k1+k2−(CCA/2)/G(70)  Equation 6
Where V_init70=the initial or instantaneous voltage predicted at full charge and 70° F. and G(70) is the projected conductance at full charge and 70° F.

[0035] As mentioned above, the load test must sustain its load for a period of time (15 seconds). For good batteries, the initial voltage (2-second voltage) and the 15-second voltage are not substantially different. However, as a battery approaches the end of life, its voltage can decay markedly during the discharge, thus causing a failure even though the initial voltage may be above the minimum specification level. This decay between the initial voltage and the 15-second voltage can be linearly related to the initial battery voltage at standard temperature for most batteries. Thus the decay voltage (DV) can be estimated by using the following relationship:
DV=k3*V_init70−k4  Equation 7
where V_init70 is the initial or instantaneous load test voltage at 70° F. and k3 and k4 are constants.

[0036] Combining the above Equations, the load test voltage (LTV) at a standard test temperature of 70° F. can be estimated as:
LTV₇₀=V_init70−DV
or
LTV₇₀=k4+LTV₇₀*(1−k3)  Equation 8
This value can then be compared to the rated load test voltage for the battery at the standard test temperature and a judgment on the state of health of the battery can be easily rendered. The rated load test voltage of 9.6 Volts at 70° F. for 12V batteries is used as a comparison. It can also be appreciated that the load test voltage at any other temperature of the battery can similarly be predicted.

[0037] FIG. 2 is a flowchart 100 showing steps of a method of programming battery tester 16 in accordance with an embodiment of the present invention. As shown in flow chart 100, at step 102, a characteristic curve for the variation of battery conductance with temperature is established. At step 104, the characteristic conductance-temperature curve is programmed into memory 60 of battery tester 16 via input 66. At step 106, mathematical relationships to estimate the load test voltage from the conductance, temperature, OCV and CCA rating of the battery are established (Equations 1-8 above). At step 108, the mathematical relationships are programmed into memory 60 of battery tester 16. At this point, battery tester 16 is ready to estimate battery load test voltages and provide load test results for batteries.

[0038] FIG. 3 is a flowchart 150 showing steps of a method of testing a battery in accordance with an embodiment of the present invention. At step 152, dynamic parameter of the battery is measured. At step 154, an open circuit voltage of the battery is obtained. At step 156, a temperature of the battery is measured. At step 158, a cranking size rating (such as the CCA rating) of the battery is obtained. At step 160, a load test voltage of the battery is estimated as a function of the measured battery dynamic parameter, the open circuit voltage of the battery, the measured battery temperature and the cranking size rating of the battery. Different techniques, some of which are set forth above, can be employed to carry out the steps shown in the flow chart of FIG. 3 while maintaining substantially the same functionality without departing from the scope and spirit of the present invention.

[0039] In embodiments of the present invention, battery tester 16 is configured to issue a warning that the battery should be recharged before a judgment on the state of health of the battery can be rendered, if it determines that the battery is in an over discharged condition. Also, battery faults such as shorts can be determined by suitably combining the voltage and conductance information using known techniques.

[0040] Thus, a rapid test can be performed using the parameters of conductance, OCV, temperature and the CCA rating of the battery to provide data that the industry has accepted for batteries in service.

[0041] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As mentioned above, although the example embodiments of the present invention described above relate to estimating load test values from battery conductance measurements, dynamic parameters other than battery conductance may be utilized without departing from the spirit and scope of the invention. Examples of other dynamic parameters include dynamic resistances, admittance, impedance, reactance, susceptance or their combinations. In general, a dynamic parameter of the battery can be obtained measuring a response of the battery to any suitable active or passive source.