Abstract:
A method and apparatus is provided for rapidly and safely estimating the high-rate load test voltage of a storage battery utilizing open-circuit voltage, temperature and a dynamic parameter such as conductance or resistance. An output indicative of the condition of the battery is provided as a function of the estimated load test voltage of the battery compared to industry standards without the necessity to charge the battery or discharge the battery with high-rate loads using bulky load testing equipment.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   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. 

   BACKGROUND OF THE INVENTION 
   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. 
   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. 
   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:
     1) Measure the temperature of a center cell. Cover battery with a damp cloth.   2) Connect a voltmeter and load test leads to the appropriate battery terminals. Be sure the terminals are free of corrosion.   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.   4) Read and record the voltage at 15 seconds; remove the load.   5) Determine the minimum passing voltage based on the battery&#39;s test temperature:   

   
     
       
             
             
             
           
         
             
                 
             
           
           
             
               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 
             
             
                 
             
           
        
       
     
       
       6) If the test voltage is above the minimum, return the battery to service. 
       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. 
       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. 
     
  
   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&#39;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. 
   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. No. 5,945,829, issued Aug. 31, 1999, entitled MIDPOINT BATTERY MONITORING; U.S. Pat. No. 6,002,238, issued Dec. 14, 1999, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX IMPEDANCE OF CELLS AND BATTERIES; U.S. Pat. No. 6,037,751, issued Mar. 14, 2000, entitled APPARATUS FOR CHARGING BATTERIES; U.S. Pat. No. 6,037,777, issued Mar. 14, 2000, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Pat. No. 6,051,976, issued Apr. 18, 2000, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Pat. No. 6,081,098, issued Jun. 27, 2000, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,091,245, issued Jul. 18, 2000, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Pat. No. 6,104,167, issued Aug. 15, 2000, entitled METHOD AND APPARATUS FOR CHARGING A BATTERY; U.S. Pat. No. 6,137,269, issued Oct. 24, 2000, entitled METHOD AND APPARATUS FOR ELECTRONICALLY EVALUATING THE INTERNAL TEMPERATURE OF AN ELECTROCHEMICAL CELL OR BATTERY; U.S. Pat. No. 6,163,156, issued Dec. 19, 2000, entitled ELECTRICAL CONNECTION FOR ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,172,483, issued Jan. 9, 2001, entitled METHOD AND APPARATUS FOR MEASURING COMPLEX IMPEDANCE OF CELL AND BATTERIES; U.S. Pat. No. 6,172,505, issued Jan. 9, 2001, entitled ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,222,369, issued Apr. 24, 2001, entitled METHOD AND APPARATUS FOR DETERMINING BATTERY PROPERTIES FROM COMPLEX IMPEDANCE/ADMITTANCE; U.S. Pat. No. 6,225,808, issued May 1, 2001, entitled TEST COUNTER FOR ELECTRONIC BATTERY TESTER; U.S. Pat. No. 6,249,124, issued Jun. 19, 2001, entitled ELECTRONIC BATTERY TESTER WITH INTERNAL BATTERY; U.S. Pat. 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. 
   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. 
   SUMMARY OF THE INVENTION 
   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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified schematic diagram showing battery test circuitry in accordance with the present invention. 
       FIG. 2  is a simplified block diagram showing the steps of a method of programming a battery tester in accordance with the invention. 
       FIG. 3  is a simplified block diagram showing the steps of a method of testing a battery in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   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. 
     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. 
   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 C 1  and C 2 . 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 . 
   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 C 1  and C 2 , 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 . 
   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 . 
   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: 
                 Conductance   =     G   =       Δ   ⁢           ⁢   I       Δ   ⁢           ⁢   V                 Equation   ⁢           ⁢   1               
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.
 
   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. 
   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. 
   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.
 
   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*f 1( T,OCV )  Equation 3
 
 G   70   =Gcomp*f 2(70)/ f 2( T )  Equation 4
 
where Gcomp is conductance compensated to full charge at the OCV and temperature of the battery, G 70  is conductance at full charge and 70° F., f 1 (T,OCV) is a function to compensate the conductance at a given temperature and voltage, and f 2 (T) is a function of the specific conductance at a given temperature.
 
   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. 
   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   =k 1 *T+k 2  Equation 5
 
where T is the battery temperature and k 1  and k 2  are constants.
 
   Thus the instantaneous load test value at a standard test temperature (70° F.) can be predicted using the combined equations:
 
 V   init70 =70* k 1 +k 2−( 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.
 
   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=k 3* V   init70   −k 4  Equation 7
 
where V init70  is the initial or instantaneous load test voltage at 70° F. and k 3  and k 4  are constants.
 
   Combining the above Equations, the load test voltage (LTV) at a standard test temperature of 70° F. can be estimated as:
 
 LTV   70   =V   init70   −DV  
 
or
 
 LTV   70   =k 4 +LTV   70 *(1 −k 3)  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.
 
     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. 
     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. 
   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. 
   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. 
   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.