1. start

2. OBJECTIVES: After studying Chapter 39, the reader should be able to:
Describe how a battery works.
List the precautions necessary whenever working with batteries.
Explain how to safely charge a battery.
Discuss how to perform a battery drain test.

3. KEY TERMS:
absorbed glass mat (AGM) battery • ampere-hour (Ah) rating • antimony
battery electrical drain test • BCI
calcium • cells • cold-cranking amperes (CCA) • conductance testing • cranking amperes (CA)
deep cycling • dynamic voltage electrolyte • element
flooded cell battery
Continued

4. KEY TERMS: gassing • gell battery • grids ignition off draw (IOD) test
jump-starting
lead dioxide (peroxide) • lead sulfate • load test • low-water-loss battery
maintenance-free battery • marine cranking amperes (MCA) • meniscus
open circuit battery voltage test
Continued

5. KEY TERMS:
parasitic load test • partitions • pasting • porous lead radial-grid design • recombinant design battery • reserve capacity (RC)
sealed lead-acid (SLA) battery • sealed valve regulated (SVR) battery • sediment chamber • separators • specific gravity • sponge lead
valve regulated lead-acid (VRLA) battery

6. Everything electrical in a vehicle receives its current from the battery.
The battery is one of the most important parts of a vehicle and is the foundation for the entire electrical system.

7. PURPOSE OF A BATTERY
The primary purpose of an automotive battery is to provide a source of electrical power for starting and for electrical demands that exceed generator output. The battery is a voltage stabilizer because it acts as a reservoir where large amounts of current (amperes) can be removed quickly during starting and replaced gradually by the generator during charging. The battery must be in good (serviceable) condition before the charging system and the cranking system can be tested. It is important to test the vehicle battery before further testing of the cranking or charging system.

8. BATTERY CONSTRUCTION
Most automotive battery cases (container or covers) are constructed of polypropylene, a thin (approx inch [.0 millimeters] thick), strong, and lightweight plastic. Industrial and truck batteries are constructed of a hard, thick, rubber material.
Inside the case are six cells (for 12-volt), each with positive and negative plates. Built in the bottom are ribs to support the lead-alloy plates and provide space for sediment to settle.
Figure 39–1 Batteries are constructed of plates grouped into cells, installed in a plastic case.
This sediment chamber, prevents spent material from causing a short circuit between the plates at the bottom of the battery.
Continued

9. GRIDS
Each positive and negative plate in a battery is constructed on a framework or grid of lead. Lead is soft and must be strengthened by adding antimony or calcium for battery use. Grids hold the active material and provide electrical pathways for the current created in the plate. Maintenance-Free versus Standard Battery Grids A normal battery uses up to 5% antimony in the plate grids to add strength. The more amount of antimony, the more gassing (hydrogen and oxygen gases released), and the more water the battery will use. Maintenance-free batteries use calcium instead of antimony, because 0.2% calcium has the same strength as 6% antimony.
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10. Low-maintenance batteries use a low percentage of antimony (about 2% to 3%) or antimony only in positive plates and calcium for negative plates. The percentages that make up the alloy of the plate grids constitute the major difference between standard and maintenance-free batteries. Chemical reactions inside each battery are identical regardless of type of grid material used. Radial-Grid Design Some batteries use a grid design with only vertical and horizontal strips. The battery plate creates electricity from chemical energy, and this current must flow from where it is generated to where it connects to the outside battery post. The current must move over and up along the grid strips.
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11. A grid with a radial-grid design has lower resistance and can provide more current more rapidly than can the non-radial-grid design used in conventional batteries.
Figure 39–2 A radial grid from a battery used in both positive and negative plates.
The radial spokes act as a superhighway system for the current to travel from all areas of the grid to the battery post.
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12. Positive versus Negative Plates The positive plates have lead dioxide (peroxide) placed on the grid frame, called pasting. This dark brown active material can react with sulfuric acid of the battery. The negative plates are pasted with pure porous lead, or sponge lead, and are gray in color. Separators The positive and the negative plates must be installed alternately next to each other without touching. Nonconducting separators are used. These separators are porous and have ribs facing the positive plate. Many batteries use envelope-type separators that encase the entire plate and help prevent any material that may shed from the plates from causing a short circuit between plates at the bottom of the battery
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13. Cells Constructed of positive and negative plates, cells have insulating separators between each plate. A cell is also called an element, and is actually a 2-volt battery, regardless of number of positive or negative plates used. The greater the number of plates used in each cell, the greater the amount of current that can be produced. Typical batteries contain four positive plates and five negative plates per cell. A 12-volt battery contains six cells connected in series, producing 12 volts (6  2 = 12) and has 54 plates (9 plates per cell  6 cells). If the same battery had five positive plates and six negative, 11 plates per cell (5 + 6), or 66 plates (11 plates  6 cells), it would have the same voltage, but the amount of current (amps) the battery could produce would be increased.
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14. Partitions Cells are separated from other cells by partitions, made of the same material as the outside case of the battery. Electrical connections between cells are provided by lead connectors that loop over the top of the partition and connect the plates of the cells together. Many batteries connect the cells directly through the partition connectors, which provides the shortest path for the current and the lowest resistance. Older-style truck and industrial batteries commonly used connectors that extended through the top of the case and over and then down through the case to connect the cells.
See Figure 39–3.
Continued

15. Battery capacity is determined by the amount of active plate material in the battery and the area of the plate material exposed to the liquid, called electrolyte, in the battery.
Figure 39–3 A cutaway battery showing the connection of the cells to each other through the partition.
Some water (H2O) escapes during charging as a result of the gassing produced by the chemical reactions.
Only pure distilled water should be added to a battery. If distilled water is not available, clean drinking water can be used.

16. Electrolyte The electrolyte used in automotive batteries is a solution (liquid combination) of 36% sulfuric acid and 64% water. This used for both lead-antimony and lead-calcium (maintenance-free) batteries. The chemical symbol for this sulfuric acid solution is H2SO4.
H = Symbol for hydrogen (subscript 2 means there are two atoms of hydrogen)
S = Symbol for sulfur
O = Symbol for oxygen (subscript 4 indicates four atoms of oxygen) Electrolyte is sold premixed in the proper proportion and is factory installed. Additional electrolyte must never be added to a battery after the original electrolyte fill.

17. HOW A BATTERY WORKS
A fully charged lead-acid battery has a positive plate of lead dioxide (peroxide) and a negative plate of lead surrounded by a sulfuric acid solution (electrolyte). Difference in potential (voltage) between lead peroxide and lead in acid is approximately 2.1 volts. During Discharging The positive-plate lead dioxide (PbO2) combines with the SO4 from the electrolyte and releases its O2 into the electrolyte, forming H2O. The negative plate also combines with the SO4 from the electrolyte and becomes lead sulfate (PbSO4).

18. Figure 39–4 Chemical reaction for a lead-acid battery that is fully charged being discharged by the attached electrical load.
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19. The Fully Discharged State When the battery is fully discharged, both the positive and the negative plates are PbSO4 (lead sulfate) and the electrolyte has become water (H2O). It is usually not possible for a battery to become 100% discharged. However, as the battery is being discharged, the plates and electrolyte approach the completely dead situation. There is also the danger of freezing when a battery is discharged, because the electrolyte is mostly water. During Charging The sulfate ion (acid) leaves both the positive and the negative plates and returns to the electrolyte, where it becomes normal-strength sulfuric acid solution. The positive plate returns to lead dioxide (PbO2) and the negative plate is again pure lead (Pb). See Figure 39–5.
Continued

20. Figure 39–5 Chemical reaction for a lead-acid battery that is fully discharged being charged by the attached generator.
Continued

21. An Easy Way to Remember Battery Chemical Reactions
A battery engineer explains to the employees of the plant how a battery works using these very easy-to-remember statements:
When the battery is being discharged, the acid leaves the liquid and is de-posited on the plates. When the battery is being charged, the current flows into the battery, forcing the acid from the plate and back into the liquid (electrolyte).
An Easy Way to Remember Battery Chemical Reactions
When the battery is charged, the acid (SO4 ) is in the liquid.
When the battery is discharged, the acid (SO4 ) is on the plates.

22. SPECIFIC GRAVITY
Sulfate in the electrolyte is indicated by the electrolyte’s specific gravity, the ratio of weight of a given volume of a liquid to the weight of an equal volume of water. The more dense the material (liquid), the higher its specific gravity. Pure water is the basis for this measurement and is given a specific gravity of at 80°F. Pure sulfuric acid has a specific gravity of 1.835; the correct concentration of water and sulfuric acid (called electrolyte—64% water, 36% acid) is to at 80°F. The higher the battery’s specific gravity, the more fully it is charged. See Figure 39–6.
Continued

23. Figure 39–6 As the battery becomes discharged, the specific gravity of the battery acid decreases.

24. CHARGE INDICATORS
Some batteries are equipped with a built-in state-of-charge indicator. This indicator is simply a small ball-type hydrometer that is installed in one cell.
When the ball floats, it appears in the hydrometer’s sight glass, changing its color.
Figure 39–7 Typical battery charge indicator. If the specific gravity is low (battery discharged), the ball drops away from the reflective prism. When the battery is charged enough, the ball floats and reflects the color of the ball (usually green) back up through the sight glass and the sight glass is dark.

25. Figure 39–8 Cutaway of the battery showing the charge indicator
Figure 39–8 Cutaway of the battery showing the charge indicator. If the electrolyte level drops below the bottom of the prism, the sight glass shows clear (light). Most battery manufacturers warn that if the electrolyte level is low on a sealed battery, the battery must be replaced. Attempting to charge a battery that has a low electrolyte level can cause a buildup of gases and possibly an explosion.
This hydrometer uses a plastic ball that floats if electrolyte density is sufficient (when the battery is about 65% charged).
Because it is only testing one cell out of six, and because the hydrometer ball can easily stick in one position, it should not be trusted to give accurate data about a battery’s charge.
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26. Specific Gravity versus State of Charge and Battery Voltage Values of specific gravity, state of charge, and battery voltage at 80°F (27°C) are shown here:
See this chart on Page 406 of your textbook.

27. VALVE-REGULATED LEAD ACID BATTERIES
There are two basic types of valve regulated lead-acid (VRLA), also called sealed valve regulated (SVR) or sealed lead-acid (SLA), batteries. They use a low-pressure venting system that releases excess gas and automatically reseals if a buildup of gas is created due to overcharging. The two types include the following:
Absorbed glass mat (AGM) The acid used in an absorbed glass mat (AGM) battery is totally absorbed into the separator, making the battery leakproof and spillproof. The battery is assembled by compressing the cell about 20% then inserting it into the container. The compressed cell helps reduce damage caused by vibration and helps keep the acid tightly against the plates.
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28. Unlike conventional batteries, called flooded cell batteries, most of the hydrogen and oxygen given off during charging remains inside the battery. AGM batteries also have a longer service life, often lasting 7 to 10 years.
Absorbed glass mat batteries are used as standard equipment in vehicles such as the Chevrolet Corvette.
Figure 39–9 An absorbed glass mat battery is totally sealed and is more vibration resistant than conventional lead-acid batteries.
Continued

29. Gelled electrolyte batteries
Gelled electrolyte batteries. In a gelled electrolyte battery, silica is added to the electrolyte, which turns the electrolyte into a substance similar to gelatin. This type of battery is also called a gel battery.
Both types of valve regulated lead-acid batteries are also called recombinant design, which means oxygen gas generated at the positive plate travels through dense electrolyte to the negative plate. When the oxygen reaches the negative plate it reacts with the lead, which consumes the oxygen gas and prevents the formation of hydrogen gas. It is because of this oxygen recombination that VRLA batteries do not use water.

30. Should Batteries Be Kept Off Concrete Floors?
All batteries should be stored in a cool, dry place when not in use. Many technicians have been warned to not store or place a battery on concrete. According to battery experts, it is the temperature difference between the top and the bottom of the battery that causes a difference in the voltage potential between the top (warmer section) and the bottom (colder section). It is this difference in temperature that causes self-discharge to occur. In fact, submarines cycle seawater around their batteries to keep all sections of the battery at the same temperature to help prevent self-discharge. Always store or place batteries up off the floor and in a location where the entire battery can be kept at the same temperature, avoiding extreme heat and freezing temperatures. Concrete cannot drain the battery directly, because the case of the battery is a very good electrical insulator.
Should Batteries Be Kept Off Concrete Floors?

31. BATTERY HOLD-DOWNS
All batteries must be attached securely to the vehicle to prevent battery damage. Normal vehicle vibrations can cause the active materials inside the battery to shed. Battery hold-down clamps or brackets help reduce vibration, which can greatly reduce the capacity and life of any battery.

32. BATTERY RATINGS
Batteries are rated according to the amount of current they can produce under specific conditions.
Cold-Cranking Amperes Every automotive battery must be able to supply power to crank the engine in cold weather and provide voltage high enough to operate the ignition system for starting. The cold-cranking power of a battery is the number of amperes that can be supplied by a battery at 0°F (18°C) for 30 seconds while the battery still maintains a voltage of 1.2 volts per cell or higher. Cold-cranking performance rating is called cold-cranking amperes (CCA). Try to purchase a battery with the highest CCA for the money. See vehicle specifications for recommended capacity.
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33. Cold-Cranking Amperes Every automotive battery must be able to supply electrical power to crank the engine in cold weather and still provide battery voltage high enough to operate the ignition system for starting. The cold-cranking power of a battery is the number of amperes that can be supplied by a battery at 0°F (18°C) for 30 seconds while the battery still maintains a voltage of 1.2 volts per cell or higher. This means that the battery voltage would be 7.2 volts for a 12-volt battery and 3.6 volts for a 6-volt battery. Cold-cranking performance rating is called cold-cranking amperes (CCA). Try to purchase a battery with the highest CCA for the money. See vehicle specifications for recommended capacity.
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34. What Causes a Battery to Wear Out?
Every automotive battery has a limited service life of approximately three to seven years. During the life of a battery, the active material sheds from the surface of the positive plates. This gradually limits the power of the battery. This cycling also can cause the negative plates to become sulfated, which will also cause eventual battery failure. Excessive parasitic drains also can cause a battery to fail prematurely due to constant deep cycling of the battery.
What Causes a Battery to Wear Out?
NOTE: A battery becomes sulfated when lead sulfate (SO4) remains on the plates and does not return to electrolyte when the battery is charged.

35. Cranking Amperes The designation CA (cranking amperes) refers to the number of amperes that can be supplied by a battery at 32°F (0°C). This rating results in a higher number than the more stringent CCA rating.
Figure 39–10 This battery has a cranking amperes (CA) rating of This means that this battery is capable of cranking an engine for 30 seconds at a temperature of 32°F (0°C) at a minimum of 1.2 volts per cell (7.2 volts for a 12-volt battery).
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36. Ampere-hour Rating Marine cranking amperes (MCA) are similar to cranking amperes and tested at 32°F (0°C). Another type of rating is the ampere-hour (Ah) rating, which is the number of amperes that can be discharged from the battery before dropping at 10.5 volts over a 20-hour period. A able to supply 3.75 amperes for 20 hours has a rating of 75 ampere-hours (3.75  ). Reserve Capacity The reserve capacity (RC) rating for batteries is the number of minutes for which the battery can produce 25 amperes and still have a battery voltage of 1.75 volts per cell (10.5 volts for a 12-volt battery). This rating is actually a measurement of the time for which a vehicle can be driven in the event of a charging system failure.
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37. What Determines Battery Capacity?
The capacity of any battery is determined by the amount of active material in the battery. A battery with a large number of thin plates can produce high current for a short period. If a few thick plates are used, the battery can produce low current for a long period. A trolling motor battery used for fishing must supply a low current for a long period of time. An automotive battery is required to produce a high current for a short period for cranking. Therefore, every battery is designed for a specific application.
What Determines Battery Capacity?

38. DEEP CYCLING
Deep cycling is almost fully discharging a battery and then completely recharging it. Golf cart batteries are an example of lead-acid batteries that must be designed to be deep cycled. A golf cart must be able to cover two 18-hole rounds of golf and then be fully recharged overnight. Charging is hard on batteries because the internal heat generated can cause plate warpage, so these specially designed batteries use thicker plate grids that resist warpage. Normal automotive batteries are not designed for repeated deep cycling.

39. What Can Cause a Battery to Explode? - Part 1
Batteries discharge hydrogen gas and oxygen when being charged. If there happens to be a flame or spark, the hydrogen will burn. The oxygen can also help contribute to an explosion of a small pocket of hydrogen. This is likely what happened to the battery in Figure 39–11, when the battery charger was left on the battery over 24 hours. Apparently, a small electrical arc occurred inside the battery and the resulting explosion sounded like a shotgun being fired.
Figure (a) A small spark inside the battery was the most likely cause of this battery explosion. Parts of the battery were thrown 30 feet (10 m). Luckily no one was around the vehicle at the time.

40. What Can Cause a Battery to Explode? - Part 2
Figure (b) Because battery acid was spilled and sprayed around the battery, the entire area was rinsed with water after unplugging the battery charger.

41. What Are Some Symptoms of a Weak or Defective Battery? - Part 1
There are several warning signs that may indicate that a battery is near the end of its useful life, including:
What Are Some Symptoms of a Weak or Defective Battery? - Part 1
Uses water in one or more cells—This indicates that the plates are sulfated and that during the charging process, the water in the electrolyte is being turned into hydrogen and oxygen gases.
Excessive corrosion on battery cables or connections—Corrosion is more likely to occur if the battery is sulfated, creating hot spots on the plates.
Slower than normal engine cranking—When the capacity of the battery is reduced due to damage or age, it is less likely to be able to supply the necessary current for starting the engine, especially during cold weather.

42. …Symptoms? - Part 2
When the battery is being charged, the acid fumes are forced out of the vent holes and get onto the battery cables and connections and even on the battery tray underneath the battery.
Figure 39–12 Corrosion on a battery cable could be an indication that the battery itself is either being overcharged or is sulfated, creating a lot of gassing of the electrolyte.

43. BATTERY SERVICE SAFETY CONSIDERATIONS
Batteries contain acid and release explosive gases (hydrogen and oxygen) during normal charging and discharging cycles. To prevent physical injury or vehicle damage, adhere to the following:
Whenever working on any electrical component on a vehicle, disconnect the negative battery cable from the battery. When the negative cable is disconnected, all electrical circuits in the vehicle will be open, which will prevent accidental electrical contact between an electrical component and ground. Any electrical spark has the potential to cause explosion and personal injury.
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44. Wear eye protection whenever working around any battery.
Wear protective clothing to avoid skin contact with battery acid.
Always adhere to all safety precautions as stated in the service procedures for equipment used for battery service and testing.
Never smoke or use an open flame around any battery. .

45. BATTERY MAINTENANCE
Most new-style batteries are of maintenance-free design that use lead-calcium instead of lead-antimony plate grid construction. Because lead-calcium batteries do not release as much gas as the older-style lead-antimony batteries, there is less consumption of water during normal service. Also, with less gassing, less corrosion is observed on the battery terminals, wiring, and support trays. Side-terminal battery design also has reduced the self-discharge that can often occur as a result of dirt and moisture on the top of the battery, which provide a conductive path for the current to flow between the terminals that can lead to battery discharge.
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46. Distilled water is recommended by all battery manufacturers.
Battery maintenance includes making certain the battery case is clean, checking and adding clean water if necessary.
Distilled water is recommended by all battery manufacturers.
Figure 39–13 A visual inspection on this battery showed that the electrolyte level was below the plates in all cells.
If distilled water is not available, clean ordinary drinking water, low in mineral content, can be used.
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47. Because water is the only thing in a battery that is consumed, acid should never be added to a battery. Battery electrolyte is an exact mixture of acid and water (64% water and 36% acid). Some water in the electrolyte escapes during normal operation of charging and discharging, but acid content of the electrolyte remains in the battery. Adding electrolyte increases the acid content of the electrolyte and will shorten the life of the battery. Do not overfill a battery, because normal gassing will cause the electrolyte to escape and start corrosion on battery terminals, hold-down brackets, and tray. Fill batteries to until the water becomes “puckered,” indicating the electrolyte level is even with the bottom of the filler tube. This puckering of water in a tube is called the meniscus.
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48. The battery should be secured with a hold-down bracket to prevent vibration from damaging the plates inside the battery. Factory-original hold-down brackets are often available through local automobile dealers, and universal hold-down units are available through local automotive parts stores. Battery cable connections should be checked and cleaned to prevent voltage drop at the connections. One common reason for an engine to not start is loose or corroded battery cable connections. Replacement battery cable terminal ends are available at most automotive parts stores.

49. Dynamic versus Open Circuit Voltage
Open circuit voltage is the voltage (usually of a battery) that exists without a load being applied. Dynamic voltage is the voltage of the power source (battery) with the circuit in operation. A vehicle battery, for example, may indicate it has 12.6 volts or more, but voltage may drop when the battery is put under a load such as cranking the engine. If battery voltage drops too much, the starter motor will rotate more slowly and the engine may not start. If dynamic voltage is lower than specified, the battery may be weak or defective or the circuit may be defective, resulting in too much current being drawn from the battery.
Dynamic versus Open Circuit Voltage

50. BATTERY VOLTAGE TEST
Testing the battery voltage with a voltmeter is a simple method for determining the state of charge of any battery. See Figure 39–14. The voltage of a battery does not necessarily indicate whether the battery can perform satisfactorily, but it does indicate to the technician more about the battery’s condition than a simple visual inspection. A battery that “looks good” may not be good. This test is commonly called an open circuit battery voltage test because it is conducted with an open circuit—with no current flowing and no load applied to the battery.
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51. Figure 39–14 (a) A battery voltage of 12
Figure 39–14 (a) A battery voltage of volts is definitely not fully charged and should be charged before testing. (b) A battery that measures volts or higher after the surface charge has been removed is 100% charged.
(a)
(b)
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52. Open Circuit Battery Voltage Test
If the battery has just been charged or if the vehicle has been driven recently, it is necessary to remove the surface charge from the battery before testing. A surface charge is a charge of higher-than-normal voltage that is just on the surface of the battery plates.
To remove the surface charge, turn the headlights on high beam (brights) for 1 minute, then turn the headlights off and wait2 minutes.
With the engine and all electrical accessories off, and the doors shut (to turn off the interior lights), connect a voltmeter to the battery posts. Connect the red positive lead to the positive post and the black negative lead to the negative post.
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53. See the chart on Page 409 of your textbook.
Read the voltmeter and compare the results with the following state-of-charge chart. The voltages shown are for a battery at or near room temperature (70° to 80°F or 21° to 27°C).
NOTE: If the meter reads negative, the battery has been reverse charged
(has reversed polarity) and should be replaced, or the meter has been
connected incorrectly.
See the chart on Page 409 of your textbook.

54. HYDROMETER TESTING
If the battery has removable filler caps, the specific gravity of the electrolyte also can be checked.
The specific gravity test indicates the charge state of the battery
Figure 39–15 When testing a battery using a hydrometer, the reading must be corrected if the temperature is above or below 80°F (27°C).
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55. This test also can be performed on most maintenance-free batteries because the filler caps are removable from most maintenance-free batteries (except for Delco).
It can indicate a defective battery if the specific gravity of one or more cells varies by more than from the value of the highest-reading cell.
See the chart on Page 410 of your textbook.

56. BATTERY LOAD TESTING
The most accurate test to determine the condition of any battery is the load test. Most starting and charging testers use a carbon pile to create an electrical load on the battery. The amount of the load is determined by the original capacity of the battery being tested.
Figure 39–16 This battery has cold-cranking amperes (CCA) of 550 A, cranking amperes (CA) of 680 A, and load test amperes of 270 A listed right on the top label. Note all batteries have all of this information.
The proper electrical load to be used to test a battery is one-half of the CCA rating or three times the ampere-hour rating, with a minimum of a 150-ampere load.
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57. A high-rate battery load test should take one minute.
The One-Minute Test
Load for 15 seconds to remove the surface charge.
Allow 30 seconds for the battery to recover.
Load for 15 seconds to test the battery.
Apply the load for a full 15 seconds and observe the voltmeter at the end of the 15-second period while the battery is still under load. Wait 30 seconds between tests to allow time for the battery to recover. If the battery fails the load test, recharge the battery and retest. If the load test is failed again, replacement is required.
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58. Figure 39–17 An alternator regulator battery starter tester (ARBST) automatically loads the battery with a fixed load for 15 seconds to remove the surface charge, then removes the load for 30 seconds to allow the battery to recover, and then reapplies the load for another 15 seconds. The results of the test are then displayed.
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59. A good battery should indicate above 9. 6 V
A good battery should indicate above 9.6 V. Many manufacturers recommend performing the test twice, using the first load period to remove the surface charge on the battery and the second test to provide a truer indication of the condition of the battery.
Figure 39–18 The minimum capacity test voltage varies with battery temperature.
See the chart on
Page 411 of your textbook.

60. How Should You Test a Vehicle Equipped With Two Batteries? - Part 1
Many vehicles equipped with a diesel engine use two batteries. Usually these batteries are electrically connected in parallel to provide additional current (amperes) at the same voltage.
How Should You Test a Vehicle Equipped With Two Batteries? - Part 1
To successfully test the batteries, they should be disconnected and tested separately. If just one battery is found to be defective, most experts recommend that both batteries be replaced to help prevent future problems.
Figure 39–19 Most light-duty vehicles equipped with two batteries are connected in parallel as shown. Two 500-A, 12-volt batteries are capable of supplying 1,000 amperes at 12 volts, which is needed to start many diesel engines.

61. How Should You Test a Vehicle Equipped With Two Batteries? - Part 2
Because the two batteries are electrically connected, a fault in one battery can cause the good battery to discharge into the defective battery, affecting both batteries even if just one battery is at fault.
Figure 39–20 Many heavy-duty trucks and buses use two 12-volt batteries connected in series to provide 24 volts.

62. ELECTRONIC CONDUCTANCE TESTING
GM, Chrysler and Ford specify an electronic conductance tester be used to test batteries in vehicles still under factory warranty. This sends a signal through the battery and the conductance of the cells are determined by the electronics and program in the unit. The unit can determine the CCA, state-of-charge, and voltage of the battery.
The tester determines the following:
Good battery—the battery can return to service
Charge and retest—fully recharge battery and return to service
Replace the battery—battery not serviceable; should replace
Bad cell—replace—battery not serviceable; should be replaced
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63. Figure 39-21 A conductance-type battery tester
Figure A conductance-type battery tester. (a) The up-and-down arrow keys are used to answer questions about the battery before it is tested. (b) This battery shows a calculated CCA of 729 amperes and a voltage of volts. The display indicates that the battery is good, but should be charged before returning the vehicle to service. (c) A test code is displayed for warranty record-keeping purposes.
(a)
(c)
(b)

64. BATTERY CHARGING
If the state of charge of a battery is low, it must be recharged. It is best to slow-charge any battery to prevent possible overheating damage to the battery.
It may take 8 hours or more to charge a fully discharged battery.
Figure 39–22 Battery charging guide. Battery charging times vary according to state-of-charge, temperature, and charging rate.
See the chart on Page 413 of your textbook.
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65. CAUTION: Always use a battery charger designed for absorbed glass mat (AGM) batteries because that type of battery can be damaged if charged above 15.5 volts. While AGM batteries can be charged at a high average rate (about 75% amp hour rating) the voltage must be lower than the conventional charger.
Most batteries should be charged at a rate equal to 1% of the battery’s CCA rating.
CAUTION: Test results can be incorrectly reported on the display if improper, unclean connections to the battery are made. Also be sure the ignition switch and all accessories are in the off position.
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66. When charging a maintenance-free (lead-calcium) battery, the initial charge rate should be about 35 amps for 30 minutes to help start the charging process.
Fast-charging increases the amount of gassing (release of hydrogen and oxygen), which can be a health and fire hazard.
It also increases the temperature of the battery and can cause warping of the plates inside the battery.
Figure 39–23 A typical industrial battery charger. Be sure that the ignition switch is in the off position before connecting any battery charger. Connect the cables of the charger to the battery before plugging the charger into the outlet. This helps prevent a voltage spike that could occur if the charger happened to be accidentally left on. Always follow the battery charger manufacturer’s instructions.

67. Always Use Adapters on Side-Post Batteries
Side-post batteries require an adapter to be used whenever charging the battery if it is removed from the vehicle. If a bolt is threaded into the terminal, only the parts of the threads that contact the battery terminal will be conducting all of the charging current. An adapter or a bolt with a nut attached is needed to achieve full contact with the battery terminals.
Figure 39–24 Adapters should be used on side-terminal batteries when charging.

68. JUMP-STARTING
To jump-start another vehicle with a dead battery, connect good-quality copper jumper cables using another vehicle or a battery jump box.
The last connection should always be on the engine block or on an engine bracket as far from the battery as possible.
Figure 39–25 A typical battery jump box used to jump-start vehicles. These hand-portable units have almost made jumper cables obsolete.
It is normal for a spark to be created when jumper cables complete the jumping circuit, and this spark could cause an explosion of battery gases.
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69. Many newer vehicles have special ground connections built away from the battery just for the purpose of jump-starting. Check the owner’s manual or service information for the exact location.
CAUTION: To help avoid the possibility of a voltage surge causing damage to the computer or electronic circuits of the vehicle, be sure that the ignition is in the off position of both vehicles before attaching the jumper cables. After the last connection has been made, start the good vehicle, and then start the disabled vehicle.

70. BATTERY DATE CODES
Major battery manufacturers stamp codes on the battery case that give date of manufacture and other information. Most use a number to indicate year of manufacture and a letter to indicate month of manufacture, skipping letter I, as it can be confused with number 1.
The shipping date is usually indicated by a sticker to indicate month and year.
A = January
B = February
C = March
D = April
E = May
F = June
G = July
H = August
J = September
K = October
L = November
M = December
Figure 39–26 The date 5/07 indicates that this battery was shipped from the manufacturing plant in May 2007.
Continued

71. It Could Happen To You! - Part 1 of 3
After the owner of a Toyota replaced the battery, the owner noted the amber “airbag” warning lamp was lit and the radio was locked out.
It Could Happen To You! - Part 1 of 3
The owner had purchased the vehicle used from a dealer and did not know the four-digit security code needed to unlock the radio. Determined to fix the problem, the owner tried three four-digit numbers, hoping one of them would work. After three tries, the radio became permanently disabled. Frustrated, the owner went to a dealer. It cost over $300 to fix the problem.
A special tool was required to easily reset the airbag lamp. The radio had to be removed and sent out of state to an authorized radio service center and then reinstalled into the vehicle.
Before disconnecting the battery, please check with the owner to be certain that the owner has the security code for a security-type radio. A “memory saver” may be needed to keep the radio powered up when the battery is being disconnected.

72. It Could Happen To You! - Part 2 of 3
Figure 39–27 (a) Memory saver. The part numbers represent components from Radio Shack.

73. It Could Happen To You! - Part 3 of 3
Figure 39–27(b) A schematic drawing of the same memory saver. Some experts recommend using a 12-volt lantern battery instead of a small 9-volt battery to help ensure that there will be enough voltage in the event that a door is opened while the vehicle battery is disconnected. Interior lights could quickly drain a small 9-volt battery.

74. BATTERY ELECTRICAL DRAIN TEST
The battery electrical drain test determines if some component or circuit in a vehicle is causing a drain on the battery when everything is off. This test is also called the ignition off draw (IOD) or parasitic load test. This test should be performed whenever one of the following conditions exists:
Whenever a battery is being charged or replaced (a battery drain could have been the cause for charging or replacing the battery)
Whenever the battery is suspected of being drained

75. PROCEDURE FOR BATTERY ELECTRICAL DRAIN TEST
The fastest and easiest method to measure battery electrical drain is to connect an inductive DC ammeter that is capable of measuring low current (10 mA). Here is an example of a clamp-on digital multimeter being used to measure battery drain.
Figure 39–28 This mini clamp-on digital multimeter is being used to measure the amount of battery electrical drain that is present. In this case, a reading of 20 mA (displayed on the meter as 00.02A) is within the normal range of 20 to 30 mA. Be sure to clamp around all of the positive battery cable or all of the negative battery cable, whichever is easiest to get the clamp around.
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76. Procedure for battery electrical drain test using a test light:
Make certain that all lights, accessories, and ignition are off.
Check all vehicle doors to be certain that the interior courtesy (dome) lights are off.
Disconnect the negative () battery cable and install a parasitic load tool as shown here.
Start the engine, drive vehicle about 10 min, using lights, accessories and radio.
Figure 39–29 After connecting the shutoff tool, start the engine and operate all accessories. Stop the engine and turn off everything. Connect the ammeter across the shutoff switch in parallel. Wait 20 minutes. This time allows all electronic circuits to “time out” or shut down. Open the switch—all current now will flow through the ammeter. A reading greater than specified (usually greater than 50 milliamperes [0.05 amperes]) indicates a problem that should be corrected.
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77. Maximum allowable—50 mA (0.05 A)
Turn off the engine and all accessories including the under-hood light.
Connect an ammeter across the parasitic load tool switch and wait 10 minutes for all computers and circuits to shut down.
Open the switch on the load tool and read the battery electrical drain on the meter display.
Results:
Normal—10 to 30 mA (0.02 to 0.03 A)
Maximum allowable—50 mA (0.05 A)
CAUTION: Using a voltmeter to measure battery drain is not recommended by most vehicle manufacturers. The high internal resistance of the voltmeter results in an irrelevant reading that does not provide the technician with adequate information about a problem.
Continued

78. Be sure to reset the clock and antitheft radio if equipped.
Figure 39–30 The battery was replaced in this Acura and the radio displayed “code” when the replacement battery was installed. Thankfully, the owner had the five-digit code required to unlock the radio.

79. NOTE: Many electronic components draw a continuous, slight amount of battery current the ignition is off. These components include:
These components may cause a voltmeter to read full battery voltage if it is connected between the negative battery terminal and the removed end of
the negative battery cable.
Digital clocks
Electronically tuned radios for station memory and clock circuits (if the vehicle is so equipped)
The engine control computer (if the vehicle is so equipped), through slight diode leakage
The generator (alternator), through slight diode leakage.

80. FINDING THE SOURCE OF THE DRAIN
If there is a drain, check and temporarily disconnect the following:
Light under the hood
Glove compartment light
Trunk light
If after disconnecting all three of these components the battery drain can draw more than 50 milliamperes (0.05 A), disconnect one fuse at a time and leave it disconnected until the draw is reduced. Continue to disconnect the power-side wire connectors from each component included in that particular circuit until the test light goes off. The source of the battery drain can then be traced to an individual component or part of one circuit.

81. WHAT TO DO IF BATTERY DRAIN STILL EXISTS
If all the fuses have been disconnected and the drain still exists, the source of the drain has to be between the battery and the fuse box. Common sources of drain under the hood include the following:
The generator Disconnect generator wires and retest. If the excessive battery drain stops, the problem is a defective diode(s) in the generator.
The starter solenoid (relay) or wiring near its components. A common source of battery drain, due to high current flows and heat, which can damage wire or insulation.

82. HIDDEN BATTERIES
Many vehicle manufacturers today place the battery under the backseat or under the front fender. Often, the battery is not visible even if it is located under the hood.
Whenever testing or jump-starting a vehicle, look for a battery access point as shown here.
Figure 39–31 Many newer vehicles have batteries that are sometimes difficult to find. Some are located under plastic panels under the hood, under the front fender, or even under the rear seat. The jump-start instructions indicate that the spare tire hold-down bolt is to be used as the ground connection if jump-starting is necessary.

83. A discharged or defective battery has lower voltage potential than a good battery that is at least 75% charged. A weak battery could prevent the charging voltage from reaching the voltage regulator cutoff point. This lower voltage could be interpreted as indicating a defective generator (alternator) and/or voltage regulator. If the vehicle continues to operate with low system voltage, the stator winding in the generator (alternator) can be overheated, causing alternator failure.
Why Should a Discharged Battery Be Recharged or Replaced Before Further Testing?

84. BATTERY SYMPTOM GUIDE
See this guide on Page 416 of your textbook.

85. SUMMARY
Maintenance-free batteries use lead-calcium grids instead of lead antimony grids to reduce gassing.
When a battery is being discharged, the acid (SO4) is leaving the electrolyte and being deposited on the plates. When the battery is being charged, the acid (SO4) is forced off the plates and back into the electrolyte.
Batteries are rated according to CCA and reserve capacity.
All batteries should be securely attached to the vehicle with hold down brackets to prevent vibration damage.
Continued

86. SUMMARY
(cont.)
Batteries can be tested with a voltmeter to determine the state of charge.
A battery load test loads the battery to one-half of its CCA rating.
A good battery that is at least 75% charged should be able to maintain higher than 9.6 volts for the entire 15-second test period.
A battery drain test should be performed if the battery runs down.

87. end