BATTERY (AND DC POWER) SOLUTIONSThiscatalogfeaturesacomprehensivelookattheimportanceofbatteriesandroutinebatterytestingandmaintenance. In addition to this reference guide, you can go to our website anytime . . . www.avointl.com . . .for the latest in new battery testing products, applications, and other helpful ideas.COME HOME TO AVO!WWW.AVOINTL.COMIts your on-line resource book when you need electrical testing and maintenance equipment, applications andinformation. 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MEGGER, BIDDLE , and MULTI-AMPis provided.Our Web Site Continues to ExpandVisit our web site regularly because new features and capabilities are being added all the time.1WHY TEST BATTERY SYSTEMSBatteries are complex chemical mechanisms. No matter how well bat-teries are manufactured, there is still some amount of black art to them(and all chemical processes). A battery is basically two dissimilar met-als in an electrolyte. In fact, you can put a penny and a nickel in half of agrapefruit and you now have a battery. Obviously,an industrial batteryismoresophisticatedthanagrapefruitbatteryandisnotwithoutitsmaintenance needs. A good battery maintenance program may prevent,or at least, reduce the costs and damage to critical equipment due to anac mains outage.Volta invented the battery in 1800. Plant perfected the lead-acid bat-tery in 1859. It was a good design then, but with refinements over thedecades,ithasbecomeacriticallyimportantback-uppowersource.Therefinementsincludeimprovedalloys,griddesigns,jarandcovermaterialsandimprovedjar-to-coverandpostseals.Themostrevolu-tionary development was the valve-regulated battery. Nickel-cadmiumhas seen many of the same types of changes over the years.Lead-acid OverviewThe basic chemical reaction is:PbO2 + Pb + 2H2SO42PbSO4 + 2H2 + 2O2in a sulfuric acid electrolyte, where the sulfate of the acid is part of thereaction.Theacidisdepletedupondischargeandregenerateduponrecharge. Hydrogen and oxygen form during recharge and float charg-ing.In flooded batteries, they escape and water must be periodicallyadded.In sealed batteries, they recombine to form water. In valve-regu-lated lead-acid batteries, the acid is immobilized by an absorbed glassmatte (AGM). The matte is much like the fiberglass insulation in yourhouse. It traps the hydrogen and oxygen formed during discharge andallowsthemtomigratesothattheyreactbacktoformwater.Thisiswhy VRLA never need water added compared to flooded (vented) lead-acid batteries. A battery isalternating positive and negative plates sepa-ratedbymicroporousrubberinfloodedlead-acidorabsorbedglassmatte in VRLA or plastic sheeting in NiCd.All of the like-polarity platesare welded together and to the post.In the case of VRLA cells, somecompressionoftheplate-matte-platesandwichisexertedtomaintaingood contact between them.There is also a self-resealing pressure re-lief valve to vent gases when over-pressurization occurs.Lead-acid (flooded) Failure Modes Positive grid corrosion Sediment (shedding) buildup Top lead corrosion Plate sulphation Hard shorts (paste lumps)Why Test Systems: To insure the supported equip-ment is adequately backed-up. To prevent unexpected failures. To forewarn death.Battery systems are installedfor only two reasons: To protect and support criticalequipment during an ac outage. To protect revenue streams dueto the loss of service.There are only four questionsa battery user will ask. Thefirst two are very important: What is the capacity of the bat-tery now? When will it need to be replaced? What is its condition now?Whatcanbedonetoimprove,not reduce its life?There are several main typesof batteries with subtypes: Lead-acid Flooded Lead-calcium Lead-antimony VRLA (sealed) AGM Gel Flat plate Tubular Nickel-cadmium Flooded Sealed Pocket plate Flat plate2Figure 1: Changes in impedance as a result of battery capacityEach battery type has many failure modes, some of which are more preva-lent than others. In the case of flooded lead-acid, the predominant fail-ure mode is plate growth. The growth rate has been well characterizedand is taken into account when designing batteries. In many battery datasheets, there is a specification for clearance at the bottom of the jar toallow for plate growth in accordance with its rated lifetime, for example20 years.The normal failure mode is positive grid corrosion. The grids are leadalloys (lead-calcium, lead-antimony, lead-antimony-selenium) that con-vert to lead oxide over time. Since the lead oxide is a bigger crystal thanlead metal alloy, the plate grows. Battery manufacturers design for extraspace in the jars to account for this growth. At the designed end-of-lifethe plates will have grown sufficiently to pop the tops off of the batter-ies.Butexcessivecycling,temperatureandoverchargingcanalsoin-crease the speed of positive grid corrosion.Sedimentbuildup(shedding)isafunctionoftheamountofcyclingabatteryendures.ThisismoreoftenseeninUPSbatteriesbutcanbeseen elsewhere. Shedding is the sloughing off of active material from theplates, converting to white lead sulfate. Sediment buildup is the secondreason battery manufacturers have space at the bottom of the jars toallow for a certain amount of sediment before it builds-up to the point ofshorting across the bottom of the plates rendering the battery useless.The float voltage will drop and the amount of the voltage drop dependsupon how hard the short is.Shedding, in reasonable amounts, is nor-mal.Some battery designs have wrapped plates such that the sediment isheld against the plate and is not allowed to drop to the bottom. So sedi-mentdoesnotbuildupinwrappedplatedesigns.Themostcommonapplication of wrapped plates is UPS batteries.IMPEDANCE:WHAT IS IT ANDWHY IT WORKS SO WELLImpedanceisresistanceinacterms. With regard to dc batterysystems, it indicates the conditionofbatterieswithoutharmingorstressingtheminanyway.Sinceit tests the condition of the entireelectricalpathofabatteryfromterminalplatetoterminalplate,impedance can find weaknesses inthe battery easily and reliably.Applyinganactestsignaltotheterminal plates performs the test.Thenmeasureboththetotalaccurrent in the string and the volt-age drop of each unit in the stringby measuring each cell and inter-cellconnectorconsecutivelyun-tiltheentirestringismeasured.Impedanceiscalculated,dis-playedandstored.Ascellsage,the internal impedance increases(seethegraphtotheright).Bymeasuring impedance, the condi-tion of each cell in the string canbemeasuredandtrendedtode-termine when to replace a cell orthe string aiding in planning bud-getary needs.The impedance test is a true four-wire, Kelvin-type measurement toprovideexcellentreliabilityandhighly reproducible data on whichtobasesounddecisionswithre-gard to battery maintenance andreplacement.% Battery Life3Top lead corrosion, like slivering, is more of a manufacturing defect. Thisis hard to detect even with a visual inspection since it occurs near thetop of the battery and is hidden by the cover. Nearing a full failure, im-pedance may find this defect. But it will surely fail due to the high cur-rent draw when the ac mains drop off. The heat buildup when discharg-ing will most likely melt the crack open and then the entire string dropsoff-line a catastrophic failure.Plate sulphation is one of the easiest failure modes to find with imped-ance. A thorough visual inspection can sometimes find traces of platesulphation. Sulphation is the process of converting active plate materialtoinactiveleadsulfate.Sinceimpedancefindselectricalpathfailuresvery well (rather than mechanical failures, unless they are manifestedas electrical path failures), sulphation is one of the electrical path prob-lems which is easily found. Sulphation is due to low charger voltage set-tingsorincompleterechargeafteranoutage.Sulfatesformwhenthebattery is not being kept fully charged.Lead-acid (VRLA) Failure Modes Dry-out (a.k.a. Loss-of-Compression) Plate Sulphation (see above) Soft and Hard Shorts Post leakage Thermal runaway Positive grid corrosion (see above)Dry-outisaphenomenonthatoccursduetoexcessiveheat(lackofproperventilation),overcharging,whichcancauseelevatedinternaltemperatures, high ambient (room) temperatures, etc. At elevated inter-nal temperatures, the sealed cells will vent through the PRV. When suffi-cient electrolyte is vented, the glass matte no longer is in contact withthe plates, thus increasing the internal impedance and reducing batterycapacity.Insomecases,thePRVcanberemovedanddistilledwateradded (but only in worst case scenarios and by an authorized servicecompany since removing the PRV may void the warranty). This failuremode is easily detected by impedance and is one of the more commonfailure modes of VRLA batteries.Soft (a.k.a. dendritic shorts) and hard shorts occur for a number of rea-sons. Hard sorts are typically caused by paste lumps pushing throughthematteandshortingouttotheadjacent(oppositepolarity)plate.Soft shorts, on the other hand, are caused by deep discharges. When thespecificgravityoftheacidgetstoolow,theleadwilldissolveintoit.Since the liquid, and dissolved lead, is immobilized by the glass matte,when the battery is recharged, the lead comes out of solution formingdendritesinsidethematte.Insomecases,theleaddendritesshortthroughthemattetotheadjacentplate.Thefloatvoltagemaydropslightly but impedance can find this failure mode easily but is a decreasein impedance, not the typical increase as in dry-out. See Figure 1, Ab-normal Cell.IEEE RECOMMENDEDPRACTICESIEEE 450-1995IEEE Recommended Practice forMaintenance,TestingandRe-placementofVentedLead-acidBatteriesforStationaryApplica-tionsdescribesthefrequencyandtypeofmeasurementsthatneedtobetakentovalidatethecondition of the battery.The fre-quencyoftestsrangesfrommonthly to annually.Some of themonthly tests include string volt-age,appearance,ambienttem-perature, float current, etc.Quar-terly tests include specific gravity,cellvoltageandtemperature(=10% of cells).Annual tests areperformedontheentirestring.Additionally,theresistancetoground of the battery rack and in-tercell connection resistance needto be measured.Other tests madeneedtobeperformedbasedonthe values measured during peri-odic tests and battery usage (cy-cling history).IEEE 1106-1995IEEE Recommended Practice forInstallation, Maintenance, Testingand Replacement of Vented Nickel-Cadmium Batteries for StationaryApplicationshassimilarrecom-mended practices as IEEE 450.IEEE 1188-1996IEEE Recommended Practice forMaintenance,TestingandRe-placementofValve-RegulatedLead-Acid Batteries for StationaryApplicationsdefinestherecom-mendedtestsandfrequency.VRLAcellshavebeenclassifiedinto tiers of criticality of the instal-lation.The frequency and type oftests vary based on the batterystier.4Thermal runaway is when a batterys internal components melt down ina self-sustaining reaction. Normally, this phenomenon can be predictedby as much as four months which is one of the reasons why AVO Interna-tional recommends quarterly VRLA impedance testing.The impedancewill increase in advance of thermal runaway as does float current. Ther-malrunawayisrelativelyeasytoavoid,simplybyusingtemperature-compensated chargers and properly ventilating the battery room/cabi-net. Temperature-compensated chargers reduce the charge current asthe temperature increases. Remember that heating is a function of thesquare of the current.Nickel-Cadmium OverviewNiCd chemistry is similar in some respects to lead-acid in that there aretwo dissimilar metals in an electrolyte. The basic reaction is:2 NiOOH + Cd +2 H2ONi(OH)2 + Cd(OH)2inapotassiumhydroxide(alkaline)electrolyte.InNiCdbatteries,theKOH does not enter the reaction like sulfuric acid does in lead-acid bat-teries. The construction is similar to lead-acid in that there are alternat-ing positive and negative plates submerged in an electrolyte. Rarely seen,but available, are sealed NiCd batteries.Nickel-Cadmium Failure ModesNiCd batteries seem to be more robust than lead-acid. They are moreexpensive to purchase but the cost of ownership is similar to lead-acid,especially if maintenance costs are used in the cost equation. Also, therisks of catastrophic failure are considerably lower than VRLA.The failure modes of NiCd are much more limited than lead-acid. Someof the more important modes are: Gradual loss of capacity Carbonation Floating effects Cycling Iron poisoning of positive plates Service at elevated temperatures Memory effectsGradual loss of capacity occurs from the normal aging process. It is irre-versible but is not catastrophic.Carbonation is reversible and is gradual. But without proper maintenance,this can cause the load to not be supported, which can be catastrophic.This can be reversed by exchanging the electrolyte.Floating effects are the gradual loss of capacity due to long periods onfloatwithoutbeingcycled.Throughroutinemaintenance,thiscanbeavoided and is easily found by impedance testing. Floating effects arereversible by deep-cycling the battery once or twice.Iron poisoning is caused by corroding plates and is irreversible. This istypically a pocket-plate design failure mode.INSULATION RESISTANCELeaking cells can lead to reducedbatterycapacity,systemineffi-ciencies, conditions hazardous topersonnel and, in rare cases, leadto fires. A cell can leak for a vari-etyofreasonsincludingmishan-dling during shipping or installa-tion,poorpost-seals,overcharg-ing, excessive plate growth, etc.This off-line test applies a dc volt-age,say500Vdc,betweenthebuss and the rack, then measuresthe dc leakage current to calculateresistanceinMorG.Thehigher the resistance is the better.Thistestisrecommendedatin-stallationandwheneveraleakmaybesuspected(fromtelltalesigns such as salt buildup).Thistest must be performed while thebattery or cell is off-line to preventshortingthebatterysinceadcvoltage is applied to the battery.GROUND FAULTSON DC SYSTEMSWhen ground faults occur on float-ing battery systems and, in somecases, grounded systems, criticalcomponentsinthesystemmaynot operate properly. A reductionin system readiness may then oc-cur. Ground faults in excess of 100karerarelyworrisome.Some-times,inlesscriticalsystems,asinglefaultisnotworrisome,ei-ther.Butwhenthetotalgroundfaults are less than 30-50 k, sys-tem reliability is suspect.A fault is traced by applying an ac(25 Hz) current signal into the dcbuss.Simplytracethecircuitswiththehighestcurrentvaluesuntil the faults are located. Faultscan be traced easily regardless ofthe number of distribution panelsor circuits because the tracer ismerelyfollowingthestrengthoftheacsignal.Systemintegrityismaintained because it is an on-lineac test and is designed to preventsystem trips.5Poor Accuracy, Poor Repeatability (Worst Case)Excellent Accuracy, Poor Repeatability (Bad Case)Poor Accuracy, Excellent Repeatability (Better Case)Excellent Accuracy, Excellent Repeatability (Best Case)CONVERTING DATA INTOINFORMATIONWhen taking measurements, thereare two main things to know aboutaccuracy and repeatability:1. They are not the same thing2. One is more important than theother.To the left are four graphs depict-ingthedifferencebetweenaccu-racy and repeatability.Naturally,everyonewantsthebestcasebutitisnotalwayspractical to achieve. So lets makeit easy to understand. Accuracy isthe closeness of a measurement tothetruevalue,inthisexample,zero.Repeatabilityistheclose-ness of readings to each other. Thedifferencebetweenrepeatabilityandaccuracyiscalledbiaswhich can be easily calculated butonly if there is excellent precision.In the case of trending data, pre-cision is far more important sinceyouwanttomakesurethattheresultyougetisclosetothere-sult you got last time unless realchanges have truly occurred. Onlythroughsolidrepeatabilitycanonemakesurethatthetrendisduetorealchanges,notduetopoor equipment.6?FAQS ABOUT BATTERIESWhat is the value of taking specific gravity readings?Traditionally, specific gravity has not provided much value in determin-ing impending battery failure. In fact, it changes very little after the ini-tial three to six months of the batterys life. This initial change is due tothe completion of the formation process which converts inactive pastematerial into active material by reacting with the sulfuric acid.What does float voltage of a cell tell me?Float voltage indicates that the charger is working, that is, state-of-charge.Itdoesnotindicatethestate-of-health(condition)ofthecell.Itindi-cates that the cell is fully charged but dont confuse fully charged withfull capacity. There have been many times that the float voltage is withinacceptable limits and the battery fails. A low float voltage may indicatethat there is a short in the cell. This is evidenced by a float voltage atabout 2.06 or below for lead-acid (if the charger is set for 2.17 V per cell).In some cases a cell floats considerably higher than the average.Thismay be caused by the high float blotage cell compensating for anothercellthatisweakandisfloatinglow.Itispossiblethatonecellfloatsmuchhighertocompensateforseveralcellsfloatingalittlelow.Thetotal of all cells voltages must equal the charger setting.What are the recommended maintenance practices for thedifferent types of batteries?IEEE recommended (Maintenance) practices cover the three main typesof batteries: Flooded Lead-acid (IEEE 450), Valve-regulated Lead-acid (IEEE1188), and Nickel-cadmium (IEEE 1106). Generally speaking, maintenanceis essential to ensure adequate backup time. There are differing levels ofmaintenance and varying maintenance intervals depending upon the bat-tery type, site criticality, and site conditions. For example, if a site hasan elevated ambient temperature, then the batteries will age more quicklyimplying more frequent maintenance visits and battery replacements.How important is intercell connection resistance?Ourexperiencehasfoundthatmanybatteryfailuresareduetolooseintercell connections that heat up and melt open rather than cell failure.Whether a cell is weak or an intercell connector is loose, one bad appledoes spoil the whole bushel.Whenleadacidbatteriesarefrequentlycycled,thenegativeterminalmay cold flow, thus loosening the connection.What are the most common failure modes and how canimpedance find them?There are numerous failure modes, again depending upon battery type.Briefly, some failure modes for flooded are:plate sulphation, sedimentbuildup and positive grid corrosion. For VRLA, some failure modes in-clude:dry-out(loss-of-compression),positivegridcorrosionandcellleakage.PleaserefertotheBatteryFailureModesApplicationNotewhichcanbefoundontheAVOwebsite(www.avointl.com)formoredetailed information.7?How often should impedance readings be taken?The frequency of impedance readings varies with battery type, site con-ditions, and previous maintenance practices. AVO International recom-mends that VRLA batteries are measured quarterly due to their unpre-dictable nature while semiannually for NiCd and flooded lead-acid types.How do I interpret data?Therearethreegeneralmodesofdatainterpretation:instantaneous,shortterm,andlongterm.Formoredetails,pleaserefertotheDataInterpretation Application Note which can be found on the AVO website(www.avointl.com).What does ripple current tell me?Ripple current is a manifestation of the rectifier/charger which convertsac into dc. No charger is 100 percent efficient. Therefore, some ac carry-over occurs. The level of this carry-over depends upon the quality andfeatures of the charger itself. The most basic chargers do not have filtersto remove ripple components and, therefore, apply higher levels of rippletothebattery.ThisistypicalinUPSsystems.Becauseripplecreateshumontelephonelines,telcorectifiersareverywellfiltered.Asthecharger ages though, the ripple current increases.Battery manufacturers have defined a loose guideline of 6 A rms rippleforevery100Ahofbatterycapacity.Abovethislevel,heatingofthebattery may occur, thus shortening the life of the battery. The 10 A BiddleBITEs measure 60 Hz component of ripple. The 60 Hz component is wellcorrelated to total rms ripple and gives reliable data.How can I predict when I need to change a cell or the entirebattery?Eventhoughthereisnotaperfectmathematicalcorrelationbetweenbattery capacity and impedance, the amount of increase in impedanceis a strong indicator of battery health. AVO has found that a 20 percentincrease in impedance for flooded lead-acid generally correlates to 80percent battery capacity. In VRLA, that increase is closer to 50 percentfrom the batterys initial impedance or from the manufacturers baselinevalues.At what point should I stop changing cells and replace the entirebattery?In shorter strings (less than 40 cells/jars), the entire battery should bereplaced when three to five units have been replaced. In longer strings, asimilar percentage that is replaced is the criterion.FAQS ABOUT BATTERIESFor additional details on battery solutions and applications, contact thefactory directly via email:battery@avointl.com8MBITE Miniature Battery Impedance Test EquipmentThe Biddle MBITE is a lightweight, easy-to-use battery tester ideal fordetermining the health of flooded and sealed lead-acid and Ni-Cd batter-ies up to 2500 Ah in many telco, switchgear, motive power, airline, etc.applications.In addition to measuring battery impedance and interconnection resis-tance, the MBITE measures individual dc terminal voltages. Furthermore,since impedance does not stress the battery, terminal voltages do notincrease during the test and may be used for documentation purposes.Allthreeparameterscanbestored(upto1000linesofreadings)on-board for immediate review at the test site on the 3-1/2 in. LCD or fromthe built-in printer. The stored data can be downloaded via the RS-232connector to a PC using AVOLink download software or other commu-nications packages to spreadsheet applications for further analysis ordatabasing.BITE2 Battery Impedance Test EquipmentThe Biddle BITE2 is designed primarily for testing larger cells found intelco COs and MTSOs, UPS and substation. However, it also can be usedinthesmallestofbatterysystems.BecausetheBITE2hasalargermemory, more data can be stored from more sites before downloadingto a PC.A unique feature of the BITE2 is that if while in the middle of a test, youreceive an emergency call to go elsewhere, simply turn off the Receiver,pack up and go. When you return to finish the test, simply reconnect thesource current leads and turn on the Receiver. The Receiver will remem-ber where you left off. Just continue measuring from that point forward.C-BITE Compact Battery Condition TesterThe Biddle C-BITE is ideally suited to help determine the condition ofbatteriesindistributedpower(outsideplant),wireless,customerpremise, smaller telecommunications installations, emergency lightingsystems, small UPS systems, and many other smaller installation types.The C-BITE measures the internal resistance, interconnection resistance,floatvoltageandtemperature(withanoptionalprobe)ofsecondarybatteries. An ac four-wire measurement (Kelvin-type) is utilized to elimi-nateanyerrorsduetoleadwireresistance.Anotheradvantageofacresistance is that the dc voltage of the battery system does not affect it.BITE 2P Battery Impedance Test EquipmentThe Biddle BITE 2P determines the condition of lead-acid and nickel-cadmium cells up to 7000 Ah. An advanced feature set has been devel-oped that includes Pass/Warning/Fail calculations based on a user-en-tered baseline value, advanced printing functions and more. The case ofthe BITE 2P consists of both the transmitter and a carrying case for all ofthe standard accessories and some optional accessories, in an all-in-oneunit.The BITE 2P receiver stores the readings in its internal memory. Thesemeasurements, along with other maintenance data such as ambient andpilot cell temperatures and ac ripple current, assist in determining theoverall condition of battery systems.BATTERY TEST EQUIPMENTRegardlessofwhetheryouaretesting flooded lead-acid, VRLA orNi-Cd cells, AVO International hasthe right equipment for your bat-terymaintenancerequirements.The products and associated ac-cessoriesprovidesmeaningfuldata on battery health without sig-nificant expense or any reductionin remaining battery capacity.Interruption in service can causedisaster to supported equipmentand facilities. Consequently, a de-pendable backup power system iscritical so that when AC mains fail,costlyserviceinterruptionscanbeavoided.Thebatteryimped-ancetesthelpstoidentifyweakcells before they cause problems.Taking the battery off-line for test-ingistimeconsumingandaddsrisk to the process. This processisunnecessarywiththeon-linetestingcapabilitiesoftheAVOfamilyofbatterytestproducts.The highly repeatable instrumentshelp reduce downtime and avoidpersonal injury and equipment.BITE2C-BITEMBITE9Battery Ground-Fault LocatorThe Multi-Amp Battery Ground-fault Locator (BGL) is useful for locat-ing grounds on any type of battery system, including those in refineries,mines,utilities,UPS,andcontinuousprocesssystems.TheBGLoper-ates on battery systems up to 260 V dc that are either floating or groundedthrough a resistor.An additional feature of the BGL is its ability to measure battery systemtotal capacitance to ground or the capacitors of any branch of the sys-tem. This allows the operator to determine the maximum practical fault-resistance range and provides the user with information on the batterysystem.Battery Ground Fault TracerThe Biddle Battery Ground Fault Tracer (BGFT) identifies, tracks, andlocates ground faults in ungrounded dc battery systems without the needto go off-line. The BGFT speeds up fault location by eliminating trial-and-errorproceduresandisparticularlyusefulinanyindustrywhereuninterruptable power is critical. Those industries include: Power generation Utility substations UPS systems Refineries Mines Naval and shipping operations Continuous process systems Telecom backup systems Nuclear power plantsDigital Low Resistance Ohmmeters (DLROs)There are two DLROs that are very appropriate for intercell connectionresistance the Megger Ducter DLRO10 and DLRO10X. The portabil-ity of the instruments allows effortless mobility around battery strings.An automatic test mode reduces the amount of control manipulations.DH4 handspikes available with the DLRO10 and DLRO10X include indi-cator lights in one of the probes that duplicate warning and signal lightson the instrument. These lights indicate that P and C probe contact isadequate, that there is voltage across the sample under test, dischargecurrent is still flowing, and when the test is complete.In addition to its features similar to the DLRO10, the DLRO10X has theability to download test results either in real time, or after storage in onboard memory. In real time, data is output to the RS-232 port as ASCIItext, suitable for printing on a serial printer or for capture by a suitablePC program.INTERCELL CONNECTIONRESISTANCEManytimesbatteriesfailnotbe-causeofweakcellsbutduetoweak intercell connections. Torqu-ing is a mechanical method to en-sure that the electrical path resis-tance is very low. But it does nottrulyindicatethequalityoftheelectricalpathresistance.Theonlytruemethodistomeasureeachintercellconnectionresis-tancewithaDigitalLowResis-tanceOhmmeter.Additionally,itis recommended that this be donebeforethebatteryiscommis-sioned. This method will find if awasher is stuck on the No-Ox be-tweenthepostandtheintercellconnectorwhereastorquingwillnot. IEEE Recommended Practicesspecify that ten percent of the in-tercellconnectorsbemeasuredquarterly and all intercell connec-tors annually. They further specifythat the variation of intercell con-nection resistance be less than 10percent. This translates into 7 ona70-intercellconnectionresistance.Battery Ground Fault TracerDLRO10Battery Ground-fault LocatorBITE 2P