Abstract:
A live circuit battery tester allows for determining the condition of batteries under load without disconnecting the batteries and a battery charger from the load or in any way disrupting system operation during the test. Battery testing is prevented when the batteries are being used in an emergency or if they are recharging from a recent discharge. The battery tester is under microcomputer control and incorporates automatic-self diagnostics and provides a visual indication if the batteries are good or if a specific problem is detected such as if the batteries are missing, have open cells, are sulfated or are in imminent danger of failure. The battery tester determines if the charger is operating properly and tests for an open cell, bad battery connection, sulfated battery, and a weak battery and provides a visual indication of any of these problems as well as an indication of a properly operating battery.

Description:
FIELD OF THE INVENTION 
   This invention relates to apparatus for testing the status of a battery in virtually any system and is particularly directed to determining the condition of a battery (or batteries) without disconnecting the battery from the system while the battery is under load without disrupting system operation. 
   BACKGROUND OF THE INVENTION 
   Batteries used in the generation of electrical energy can take on various forms. Two of the most common forms of batteries in use today are the dry cell battery and the lead-acid storage battery. Dry cell batteries were named because the electrolyte is typically comprised of a non-spillable paste-like substance. Dry cell batteries find widespread usage in such items as flashlights, portable radios, hearing aids, and other electrical devices which are frequently carried about by a user. Lead-acid storage batteries are comprised of a lead dioxide, lead plates, and aqueous sulfuric acid all disposed within a sealed container. 
   Batteries age over time with use and thus have limited life times. In the case of rechargeable batteries, a charger is frequently connected to the battery to maintain the battery in a fully charged state. The battery may also undergo frequent testing to determine its condition and provide an indication of expected continued operation. Current battery test procedures require disconnection or removal of the battery from its operating circuit. This type of testing not only typically requires human intervention, but also frequently results in system downtime. Disconnection of the battery from its associated load may require an alternative power source for temporary use or a separate backup power system, both of which increase the cost for ensuring reliable battery powered operation. In addition, while current battery testers are capable of providing an indication of current battery status, they do not provide an indication of possible imminent battery failure such as due to sulfation. 
   The present invention addresses the aforementioned limitations of the prior art by providing a live circuit battery testing arrangement to allow for the manual or automatic testing of batteries under computer control while the batteries are under load without disconnection from or interruptions in the operation of the system. The battery and its associated charger are not disconnected from the load during the battery test procedure and an indication is provided if the tester has failed and/or the charging system is inoperative. Battery testing is prevented when the batteries are being used in an emergency operation or if the batteries are being recharged following a recent discharge. The battery tester of the present invention also tests for and provides an indication of possible future battery failure such as due to sulfation. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a battery tester which can be installed in virtually any battery system having a battery string of 12–260 volts with a capacity ranging from 25 to at least 5000 ampere hours. 
   It is another object of the present invention to allow for testing of batteries under load without disconnecting the batteries or an associated charger from the load or in any way disrupting system operation. 
   Yet another object of the present invention is to provide a battery tester which can be either manually operated or programmed to automatically test periodically and provides realtime visual indications of various potential problems such as that the batteries are missing, have an open cell(s), are sulfated, or that failure is imminent. 
   A further object of the present invention is to provide for the testing of a battery having a charger with a remote equalized input and automatically initiating an equalized cycle in the event of the detection of battery sulfation indicating possible near term battery failure. 
   A still further object of the present invention is to test the status of a battery, or plural connected batteries, and provide an indication to the battery user of either imminent failure of the battery or likely failure of the battery within a more extended period. 
   This invention contemplates an arrangement for testing a battery connected to a battery charger and/or a load comprising: a first conductor means for connecting the battery to the battery charger and/or work load under normal operating conditions allowing the battery to drive the work load and the battery charger to charge the battery; a second conductor means coupled in parallel across the first conductor means, wherein the second conductor means is nonconductive under normal operating conditions; a user selectable means responsive to an input for initiating testing of the battery; and a control/detection means coupled to the first and second conductor means and to the selectable means for conducting a battery test, wherein the control/detection means renders the first conductor means nonconductive and the second conductor means conductive during a battery test for isolating the battery from the battery charger while permitting the battery to continue to energize the work load during testing, and wherein the control/detection means applies a test load across the battery for measuring battery voltage during testing. 
   The invention further contemplates a method for testing the condition of a battery connected to a battery charger and a work load comprising the steps of measuring a first output voltage V o  of the battery; comparing the first output voltage V o  with a float voltage V F  and providing a first indication that the battery is charged if V o &gt;V F ; applying a test load to the battery and measuring a second output voltage under load V 1  and providing a second indication of an open cell in the battery if V 1&lt;0.75  Vpc volts; and comparing the second output voltage under load V 1  to a reference voltage V R , where V R &lt;V F , and providing a third indication of a good battery if V 1 &gt;V R  or a fourth indication of a weak battery if V 1 &lt;V R . 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims set forth those novel features which characterize the invention. However, the invention itself, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, where like reference characters identify like elements throughout the various figures, in which: 
       FIG. 1  is a simplified block diagram of a live circuit battery tester in accordance with the principles of the present invention; 
       FIG. 2  is a combined block and schematic diagram of a battery test controller showing connections to a battery under test as well as outputs to a user of the tester in accordance with the present invention; 
       FIG. 3  is a combined block and schematic diagram of an electronic timer analog circuit for use in the live circuit battery tester of the present invention; 
       FIG. 4  is a combined block and schematic diagram of an electronic timer digital circuit for use in the live circuit battery tester of the present invention; 
       FIG. 5  is a schematic diagram of a relay output circuit for use in the live circuit battery tester of the present invention; 
       FIG. 6  is a flowchart showing the main loop of an operating program used in the inventive live circuit battery tester carried out under the control of a microprocessor; and 
       FIGS. 7–18  are a series of flowcharts illustrating various subroutines carried out in the main loop of the operating program of the present invention as shown in  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , there is shown a simplified block diagram of a live circuit battery tester  10  in accordance with the present invention. The live circuit battery tester  10  includes a battery informer controller  14  connected to a battery  12  for testing the status of the battery. The battery informer controller  14  includes a relay output circuit  16  having first TS1 terminals  161  and second TS2 terminals  163 . A user of the live circuit battery tester  10  can connect appropriate instruments to the aforementioned TS1 and TS2 terminals  161 ,  163  for receiving various signals indicating the status of battery  12  as it is tested. A battery charger  18  can be connected across the terminals of the battery informer controller  14  for maintaining battery  12  in a charged state. During testing, the battery  12  may remain connected to one or more DC loads  22  via the battery informer controller  14 . Similarly, a DC-to-AC inverter  20  may be connected across the terminals of the battery informer controller  14  to allow the battery  12  to energize an AC load(s) which is not shown in the figure for simplicity. The DC load  22  and AC loads (not shown) remain connected to battery  12  via the battery informer controller  14  during testing of battery  12 . 
   Referring to  FIG. 2 , there is shown in simplified schematic and block diagram form additional details of the battery informer controller  14  and the manner in which it is connected to a battery undergoing testing, a battery charger and a load. The battery, battery charger and load are not shown in  FIG. 2  for simplicity. The battery informer controller  14  is connected to a battery by means of positive and negative terminals  32   a  and  32   b . The battery informer controller  14  is further connected to a battery charger by means of positive and negative terminals  34   a  and  34   b . Similarly, the battery informer controller  14  is coupled to DC and/or AC loads by means of positive and negative load terminals  36   a  and  36   b . Connected in circuit between the battery and the charger and load(s) is the combination of a blocking diode  42  and relay contacts  44  which are connected in parallel. Also connected in this circuit across the battery and between the positive and negative battery terminals  32   a  and  32   b  is the combination of relay contacts  38  and a load resister  40  which provide a voltage drop across the battery for testing purposes. Also connected in this circuit are a CR coil  52  and a DK coil  54  respectively associated with relay contacts  38  and relay contacts  44 . When power is applied to a coil, its associated relay contacts close rendering the relay contacts conductive. These circuit elements are connected to a J1 connector  45  of an electronic timer analog circuit  46  within the battery informer controller  14 . Various input signals are provided from the battery to the J1 connector  45  of the electronic timer analog circuit  46 , which signals are used in determining the status of the battery. In addition, outputs from a J2 connector  47  within the electronic timer analog circuit  46  to coils  52  and  54  and relay contacts  38  control the blocking diode  42  and relay contacts  44  in carrying out testing of a battery. 
   During normal operation when the battery is not being tested, relay contacts  44  are closed and diode  42  is non-conducting. In addition, relay contacts  38  are open and there is no voltage across resistor  40 . Under these conditions, the loads are driven by the battery and the battery is charged by the battery charger via the closed relay contacts  44  as needed. The battery test inputs are provided to the J1 connector  45  in the electronic timer analog circuit  46 . Upon either the manual or automatic selection of the battery test mode, appropriate outputs are provided from the J2 connector of the electronic timer analog circuit  46  to the relay coils  52  and  54  for opening of relay contacts  44  and closure of relay contacts  38  which places the battery voltage across resistor  40 , with test inputs provided to the electronic timer analog circuit  46  via its J1 connector  45 . During testing, the charger is disconnected from the battery because relay contacts  44  are open. But the battery remains connected to the load(s) via diode  42  and can energize the load(s) even while being tested and even if the battery charger fails. Thus, during battery testing the charger is isolated from the battery to ensure that the battery voltage and current are being measured and not system voltage and current. Following battery testing, relay contact  44  is again closed and relay contact  38  is opened. During non-testing, relay contacts  44  have been described as closed. However, the system could as easily be designed to close the relay contacts  44  during testing and open them when not testing. This later approach would require applying a voltage to the relay contacts  44  during testing only. 
   In the case of a power failure during a battery test, the battery will remain connected to the load through diode  42 , thus providing power to the load. Relay contacts  44  disposed across diode  42  can have 30–60 volt contacts with only 1 volt applied across the relay contacts in a first direction, and slightly less than 30 volts applied across the relay contacts in a second, opposed direction. The battery informer controller  14  senses the battery voltage and either sends control signals or actuates relays for the purpose of controlling the relay contacts  44  and relay contacts  38 . LEDs on an electronic timer digital circuit&#39;s control panel (described below) provide various visual indications of the operation and status of the battery being tested. The test conditions to which the battery is subjected allow various fault conditions such as an open cell, sulfated batteries, or tester failure to be determined. 
   Referring to  FIG. 3 , there is shown a schematic diagram of the electronic timer analog circuit  46  within the battery informer controller  14 . The electronic timer analog circuit  46  includes a power supply  122  coupled by means of a jumper wire  120  and a voltage divider network to the J1 connector. An input voltage to the J1 connector drives the switching power supply  122  which outputs a level +5 VDC to power the electronic timer digital circuit described below. Other inputs are provided to voltage clamping and conditioning circuitry  119  within the electronic timer analog circuit  46  which includes several Zener diodes for providing precisely controlled output voltage signals to the electronic timer digital circuit. Additional inputs to the electronic timer analog circuit&#39;s J1 connector are from the load positive bus, the load negative bus, and the switch end of the load resistor  40 . The electronic timer analog circuit  46  further includes a relay circuit  124  coupled to the J3 connector  49  for receiving digital inputs from the electronic timer digital circuit  50  for controlling the operation of the blocking diode  42  and relay contacts  38  and  44  via relay contacts within the J2 connector  47 . The electronic timer analog circuit  46  further includes the combination of an amplifier  126 , voltage divider  128 , a first and second digital-to-analog converters  130  and  132  for receiving inputs from the battery under test and providing corresponding conditioned outputs by means of a J3 connector  49  to a P3 connector  51  of the electronic timer digital circuit  50 . The J3 (jack) and P3 (plug) connectors  49 ,  51  are coupled by means of a ribbon cable  48 . 
   An outer control panel of the electronic timer digital circuit  50  is shown in  FIG. 2 , while a schematic diagram of the electronic timer digital circuit is shown in  FIG. 4 . The electronic circuit digital circuit  50  includes various LEDs for providing a visual indication of the status of a battery being tested as well as the operation of the live circuit battery tester. More specifically, the control panel of the electronic timer digital circuit  50  shown in  FIG. 2  includes a yellow test-in-process indicator  56  for indicating that a battery is currently being tested. The electronic timer digital circuit  50  further includes a green test pass indicator  60  indicating successful passing of the test administered by the live circuit battery tester by a battery. Also included in the display panel of the electronic timer digital circuit  50  is a red check battery system indicator  60  for alerting an operator to a possible problem with the battery undergoing testing. The electronic timer digital circuit further includes a red open cell indicator  62  for providing a visual indication that a battery undergoing test has an open cell. A push-to-reset button  64  is provided on the electronic timer digital circuit&#39;s display panel to allow an operator to reset the live circuit battery tester to the beginning of a test procedure. Also included on the electronic timer digital circuit&#39;s display panel is a red manual test mode indicator  74 , a red test failure indicator  76 , and a red auto equalizer indicator  78 . The auto equalizer indicator  78  illuminates when a battery fails a test, where the failure is not due to an open cell in the battery. An LED display  66  is also provided on the electronic timer digital circuit&#39;s display panel for displaying various characteristics of the battery undergoing testing as well as information regarding the status of the test being administered to the battery. The electronic timer digital circuit&#39;s display panel further includes a multi-mode select switch  72  having up and down positions for selecting various modes of operation as well as for selecting the parameters for presentation on the LED display  66 . Plural LEDs  53  below the LED display  66  on the electronic timer digital circuit&#39;s control panel provide a visual indication of the parameter presently being displayed. 
   Referring specifically to  FIG. 4 , additional details of the electronic timer digital circuit  50  will now be described. The electronic timer digital circuit  50  includes a microprocessor  96 , which in a preferred embodiment is the 8031 microprocessor, for carrying out the operations involved in the testing of a battery which are described in detail below. Microprocessor  86  generates timing signals and reads digital voltages and processes this data with respect to corresponding digital reference values. Microprocessor  86  is coupled to and drives the LED display  66  on the control panel of the electronic timer digital circuit  50  as well as first and second LEDs  82  and  84  disposed below the LED display and respectively representing DC amps and DC volts. Microprocessor  86  includes a random access memory (RAM) (not shown) for storing system constants. The electronic timer digital circuit  50  further includes a read only memory (ROM)  90  within which is stored an operating program described in detail below and which is coupled to the microprocessor  86  by means of a driver latch  88 . Another driver latch  94  within the electronic timer digital circuit  50  conditions output signals provided via a J7 connector  68  from the electronic timer digital circuit  50  to the relay output circuit  16 . The electronic timer digital circuit  50  further includes a digital switch  106  for manually setting initial conditions of the system, such as the battery tester&#39;s calibration timer, which are used to program microprocessor  86 . The electronic timer digital circuit  50  also includes the aforementioned select switch  72 , as well as the aforementioned plural LEDs  56 ,  58 ,  60 ,  62 ,  74 ,  76 ,  78  and  80  for providing a visual indication of the operation of the battery tester and the status of a battery being tested which were described in detail above. An array of logic gates  92  condition signals from the microprocessor  86  for use by either the electronic timer digital circuit  50  or by other components of the battery tester. 
     FIG. 5  is a schematic diagram of the relay output circuit  16  of the live circuit battery tester of the present invention. Relay output circuit  16  includes a DIP switch  150  which receives signals from the battery tester&#39;s electronic timer digital circuit  50  by means of J7 connector  68  and performs address decoding. Outputs from the DIP switch  150  are provided to PNP transistors  152  and  154  which, in turn, are respectively coupled to NPN transistors  158  and  156 . The output of NPN transistor  156  is provided to a first coil  160 , while the output of NPN transistor  158  is provided to a second coil  162 . First and second coils  160 ,  162  respectively drive relay contacts  164 ,  166 ,  168 ,  170  and relay contacts  172 ,  174 ,  176 ,  178  at the output of the relay output circuit  16  for controlling whether the battery tester operates in a normal test mode or an equalized test mode, or in a normal voltage mode or a high voltage mode. The relay output circuit  16  also includes TS1 connections  161  and TS2 connections  163 . A first pair of normally open contacts  164  and  168  and a second pair of normally closed contacts  166  and  170  are coupled to the TS1 connections  161 . Similarly, a first pair of normally open contacts  172  and  176  and second pair of normally closed contacts  174  and  178  are coupled to the TS2 connections  163 . Thus, the first set of relay contacts  164 ,  166 ,  168 ,  170  and the TS1 connections  161  are used in the equalize mode of operation, while the second set of relay contacts  172 ,  174 ,  176 ,  178  and the TS2 connections  163  are used in the normal test mode of operation. In the equalize test mode, the charger voltage to the battery is increased resulting in an increase in the voltage in all of the battery&#39;s cells in order to reduce battery sulfation. The equalize test mode is automatically initiated upon the detection of a weak battery. It is these normally opened and normally closed contacts coupled to the various output connections which control the outputs of the battery tester which are provided to user peripherals which are not shown in the figure for simplicity. 
   Battery tester failure is determined by measuring the voltage across the test load resistor  40  or across relay contacts  38 . The absence of a voltage across resistor  40  indicates that a test is not in process, while a voltage across the resistor indicates that a test is in process. The battery informer controller  14  monitors the voltage across resistor  40 . If it is decided to use the voltage across the relay contacts  38 , then a voltage across the relay contacts indicates that the contacts are open. If the test indicates that there is no voltage across relay contacts  38 , then the contacts are closed. The battery informer controller  14  monitors the voltage across either relay contacts  38  or resistor  40  and determines when the contacts should be opened or closed. If relay contacts  38  are in the wrong state, the battery tester has failed and an appropriate alarm is actuated. If the status of the voltage across resistor  40  indicates that a battery test is in process with the battery informer controller  14  not having initiated the test, a failure has occurred and an appropriate visual indication is provided. If the voltage indicates that no test is in process after the battery informer controller  14  has initiated a test, a failure has also occurred which is indicated by actuation of the summary alarm with an appropriate LED indication provided on the electronic timer digital circuit&#39;s front control panel. The battery charger voltage is monitored to determine if a test should be initiated. By using this voltage, a charger failure indicator may be energized with an optional relay. Charger failure is defined as the charger voltage dropping below 2.05 Vpc (low voltage), with the check battery system LED illuminating and an optional relay changing state. 
   Referring to  FIG. 6 , there is shown a main program loop in the form of a flow chart consisting of a series of steps carried out under the control of microprocessor  86  within the electronic timer digital circuit  50  in carrying out the present invention. Microprocessor  86  carries out the sequence of steps shown in the flowchart of  FIG. 6  in cooperation with other components shown in  FIG. 4 , particularly ROM  90  within which is stored the operating program for carrying out the inventive process shown in  FIG. 6 . In  FIG. 6 , each rectangular block having a pair of spaced end lines represents an operation carried out under the control of microprocessor  86 , while a simple rectangle in the figure represents system measurements made and recorded under the control of the microprocessor. Each of the individual operations, or steps, undertaken in carrying out the main program loop shown in  FIG. 6  is shown in greater detail in a respective subsequent figure and is described in detail below. 
   The main program loop is initiated by the microprocessor  86  at step  200  followed by program initialization at step  202 . The program initialization routine is shown in  FIG. 7  and begins with an initialization of the relays at step  230  followed by initialization of the LEDs at step  232 . The LED display  66  on the electronic timer digital circuit  50  is then cleared at step  234  followed by a lamp test at step  236 . The display is then tested at step  238  to verify its proper operation, followed by a initialization of program variables within the microprocessor  86  at step  240 . This is followed by the set-up of the system timers at step  242  and the initialization of program interrupts at step  244 . The initialization program then returns to the main program loop at step  246 . 
   The next step in the main program loop involves checking the meter select switch  72  on the control panel of the electronic timer digital circuit  50  at step  204 . The check meter select switch routine is shown in  FIG. 8  and begins with a reading of the status of the select switch  72  at step  248 . The operating program in the microprocessor  86  then determines the state of the switch at step  250 . If the select switch  72  is in the down position as determined at step  250 , the program proceeds to step  252  for changing the displays. The voltage and current display are set to the parameters selected by the operator. The program then returns to the main program loop at step  254 . If at step  250  it is determined that the select switch  72  is not down, the program then resets the customer calibration timer at step  256  and then returns to the main program loop at step  254 . The customer calibration timer is reset in accordance with the test parameters selected by the operator, i.e., number of battery cells being tested, amp hour rating of the battery being tested for a given current load, etc. 
   The main program loop then checks the status of the battery test switch  72  at step  206  which is shown in greater detail in  FIG. 9 . The check battery test switch routine  206  is initiated at step  258  by reading the status of the switch, followed by a determination of whether the battery test switch is in the up position at step  260 . If at step  260  it is determined that the battery test switch is not in the up position, the program proceeds to step  262  and resets the factory calibration timer and then returns to the main program loop at step  268 . If at step  260  it is determined that the battery test switch is in the up position, the program proceeds to step  264  and determines whether a battery test is currently in process. If a battery test is in process, the program proceeds to step  266 , stops the battery test, and proceeds to step  268  in executing a return to the main program loop. If at step  264 , it is determined that there is not currently a battery test in process, the program proceed to step  270  and initiates a start test sequence and then returns to the main program loop at step  268 . 
   Following the check of the battery test switch at step  206  in the main program loop, the program proceeds to step  208  and reads the output voltage of the battery under test. The LED display  66  is then updated at step  210  by determining which parameter has been selected for display and then displaying the selected parameter. Thus, as shown in  FIG. 10 , at step  272  the program determines if the voltage has been selected for display. If the voltage has been selected, a voltage is displayed at step  284 , with the program returning to the main program loop at step  282 . Similarly, at steps  274 ,  276  and  278  the program determines whether the current, amp hour capacity, or the auto test interval has been selected, respectively, followed by display of the selected parameter such as the display of current at step  286 , the display of amp hour capacity at step  288 , or the display of the auto test interval at step  290 . Following display of any of these selected parameters, the program then returns to the main program loop at step  282 . If none of the aforementioned parameters has been selected for display, the program at step  280  displays the voltage and then returns to the main program loop at step  282 . 
   Following updating of the display at step  210 , the program proceeds to step  212  for checking for selection of the automatic test mode. As shown in  FIG. 11 , the automatic test check is initiated at step  292  by a determination of whether the battery test has been selected. If the battery test has not been selected, the program returns to the main program loop at step  300 . If it is determined at step  292  that the battery test has been selected, the program proceeds to step  294  to determine if there is sufficient time to perform the test. If it is determined at step  294  that there is insufficient time to perform the battery test, the program returns to the main program loop at step  300 . If at step  294  it is determined that there is sufficient time to perform the battery test, the program proceeds to step  296  and reloads the auto test interval timers and initiates an automatic battery test at step  298 . The program then returns to the main program loop at step  300 . 
   Following checking for the selection of the auto test mode at step  212 , the program then proceeds to step  214  for testing a battery which is initiated at step  302  as shown in  FIG. 12  by a determination as to whether the battery test mode has been selected. If at step  302  it is determined that the battery test mode has not been selected, the program returns to the main program loop at step  314 . If at step  302  it is determined that a battery test has been selected, the program proceeds to step  304  for determining whether the batteries to be tested are Ni-Cad batteries. If it is determined at step  304  that the batteries to be tested are Ni-Cad batteries, the program proceeds to step  306  for battery testing and then determines at  310   a  if the measured voltage is less than 1.0 Vpc (Volts per cell). Similarly, if at step  304  it is determined that the batteries to be tested are not Ni-Cad batteries, the program at step  308  performs a lead acid battery test and proceeds to step  310   b  to determine if the measured battery voltage is less than 2.0 Vpc. If the measured voltage as determined at step  310   a  is not less than 1.0 Vpc or as determined at step  310   b  is not less than 2.0 Vpc, the program determines that the test has been passed and returns to the main program loop at step  314 . If it is determined at step  310   a  that the measured battery voltage is less than 1.0 Vpc or at step  310   b  that the measured battery voltage is less than 2.0 Vpc, the program proceeds to step  312  and provides an indication that the battery has failed the test and then returns to the main program loop at step  314 . The test mode for a Ni-Cad battery or a lead acid battery is set by the operator prior to testing by means of manual switch  106 . 
   After the initial testing of the battery at step  214 , the battery is then subjected to an open cell detection test at step  216  which is initiated at step  316  as shown in  FIG. 13  following a determination that the battery test has been selected. If battery test has not be selected as determined at step  316 , the program returns to the main program loop at step  328 . If at step  316  it is determined that battery test has been selected, the program proceeds to step  318  to determine if the batteries being tested are Ni-Cad batteries. If at step  318  it is determined that the batteries are Ni-Cad batteries, the program then proceeds to step  320  and performs the appropriate test. If at step  318  it is determined that the batteries being tested are not Ni-Cad batteries, the program proceeds to a lead acid battery test at step  322 . Following testing of Ni-Cad batteries at step  320  or lead acid batteries in step  322 , the program proceeds either to step  324   a  to determine if the measured battery voltage is less than 0.75 Vpc for Ni-Cad batteries or to step  324   b  to determine if the measured battery voltage is less than 1.0 Vpc for lead acid batteries. If at step  324   a  the measured voltage is determined to be greater than or equal to 0.75 Vpc, this indicates that the Ni-Cad batteries have successfully passed the open cell test and the program returns to the main program loop at step  328 . If at step  324   b  it is determined that the measured battery voltage is greater than or equal to 1.0 Vpc, the program determines that the lead acid batteries have successfully passed the open cell test and the program then returns to the main program loop at step  328 . If the battery fails this open cell test, a visual indication is presented at step  326  on the LED  62  of this occurrence indicating that the failed battery should be replaced immediately and the program returns to the main program loop at step  328 . 
   Following the open cell detection test, the program then proceeds to step  218  for determining whether the tests have been completed. As shown in  FIG. 14 , the test completed check is initiated at step  330  with a determination that the battery test has been selected. If the battery test has not been selected as determined in step  330 , the program returns to the main program loop at step  338 . If the battery test has been selected, the program proceeds to step  232  and determines if the time required for the test has passed. In the case shown in  FIG. 14  the test is 1 minute, but this parameter can be selected as desired by the operator prior to the test. If the time required for the test has passed, the program then proceeds to step  334  and provides an indication that the test has been passed, followed by a termination of the battery test at step  336  and a return to the main program loop at step  338 . If the battery under test passes the test, all system states and components such as the various relay contacts are cleared to their initial state or operating condition. 
   Following completion of the test completed check at step  218 , the program proceeds to step  220  for testing the delay monitor. The delay monitor test is initiated at step  340  as shown in  FIG. 15  by determining if battery test has been selected. If battery test has not been selected, the program returns to the main program loop at step  356 . If at step  340  it is determined that battery test has been selected, the program proceeds to step  342  for determining if the batteries to be tested are Ni-Cad batteries. If at step  342  it is determined that the batteries to be tested are Ni-Cad batteries, the program proceeds to step  344  for testing the Ni-Cad batteries. If at step  342 , it is determined that the batteries to be tested are not Ni-Cad batteries, the program proceeds to step  346  for testing lead acid batteries. After testing the Ni-Cad batteries at step  344  the program then determines at step  348   a  if the battery voltage is less than 1.1 Vpc. If the Ni-Cad battery voltage is greater than or equal to 1.1 Vpc, the program proceeds to step  354  for placing the battery charger in the equalize mode, followed by a return to the main program loop at step  356 . After testing the lead acid batteries at step  346 , the program then determines at step  348   b  if the battery output voltage is less than 2.05 Vpc. If it is determined that the lead acid battery output voltage is greater than or equal to 2.05 Vpc, the program proceeds to step  354  for placing the battery charger in the equalize mode, followed by a return to the main program loop at step  356 . If the lead acid battery output voltage is less than 2.05 Vpc as determined at step  348   b  or the Ni-Cad battery output voltage is less than 1.1 Vpc as determined at step  348   a , a determination is made at step  350  that the charger has failed and the program then proceeds to step  352  for delaying the next test of the battery for 12 hours. Failure of the battery charger results in illumination of an LED for alerting the operator. The program then proceeds to step  356  for returning to the main program loop. A battery not connected to anything will provide an output voltage of 2.0 Vpc. The float voltage at which a battery is charged is 2.17 Vpc. If the battery voltage is measured at less than 2.05 Vpc, it is determined that the battery charger has failed. 
   Following the monitoring for a test delay at step  220 , the main program loop then proceeds to step  222  for performing a failed tester check. The failed tester check is initiated at step  358  as shown in  FIG. 16  with a determination if the battery test has been selected. If the battery test has been selected, the program proceeds to step  362  and returns to the main program loop. If at step  358  it is determined that the battery test has not been selected, the program proceeds to step  360  and determines if there is a voltage across the contacts of the battery tester. When performing a battery test, relay contacts  38  should be closed and there should not be a voltage across the battery tester&#39;s contacts. If there is no voltage across the contacts of the battery tester as determined at step  360 , the program proceeds to step  362  and returns to the main program loop. If at step  360  it is determined that there is a voltage applied across the contacts of the battery tester, the program at step  364  then determines that the tester has failed. After determining that the tester has failed at step  364 , the program proceeds to step  366  for executing a loop until the tester is reset. This loop continues until the battery tester has been reset. 
   Following the performance of a failed tester check at step  222 , the main program loop proceeds to step  224  for monitoring the battery tester cooling time. Monitoring tester cooling time is initiated at step  368  as shown in  FIG. 17  for the purpose of determining whether a battery test has been selected. If at step  368  it is determined that the battery test has not been selected, the program proceeds to step  372  for returning to the main program loop. If at step  368  it is determined that the battery test has been selected, the program proceeds to step  370  for reloading the cooling timer constant, followed by a return to the main program loop at step  372 . The reloading of the cooling timer constant is important in the manual mode of operation to protect various electronic components such as resistors and diodes from damage due to overheating caused by excessive testing. The program then proceeds to the start test procedure at step  226  which is initiated at step  374  as shown in  FIG. 18  with a determination of whether the battery tester has cooled down sufficiently to initiate a battery test. If at step  374  it is determined that the battery tester has not cooled down sufficiently, the program then proceeds to step  378  for delaying initiation of a battery test, followed by a return to the main program loop at step  380  after the delay has expired. If at step  374  it is determined that the temperature of the battery tester is low enough to conduct a battery test, the battery test is conducted at step  376  followed by a return to the main program loop, at step  380 . Following this start test procedure carried out at step  226 , the main program loop concludes by carrying out the test completed check at step  228  which was previously described. The main program loop is then reinitiated by returning to the check meter select switch operation at step  204 . 
   While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the relevant arts that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.