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Section 2: The Battery System
2.1-- An Overview of the Battery System

To begin the topic of the battery system, we've provided you with some basic information on how the battery system functions.

Each cell of a battery consists of positive plates, negative plates, and an electrolyte solution. Batteries produce electricity because of a chemical reaction between these three elements.

Figure 3: Battery components

In a fully-charged battery, the positive plate consists of lead peroxide (the symbol PbO2), which is also called lead dioxide. Each molecule of PbO2 consists of one lead atom and two oxygen atoms. The negative plate is sponge lead (the symbol Pb), which may be composed of an alloy of antimony or calcium. The electrolyte solution is sulfuric acid (the symbol H2SO4) diluted with water (H2O).

Figure 4: Fully charged battery

When an electrical load is placed on a battery, a chemical reaction takes place. The sulfate molecules in the electrolyte break off and attach themselves to the negative and positive plates. At the same time, the oxygen atoms from the lead peroxide positive plates go into the electrolyte solution to join with the hydrogen atoms, forming H2O or water. The sulfate molecules moving to the plates and the oxygen atoms moving to the solution release energy. This is called the discharge cycle.

Figure 5: Fully discharged battery

When the battery is fully discharged, both plate are lead sulfate (the symbol PbSO4), and the solution is water. In the charging cycle, the sulfate molecules return to the solution, and the oxygen molecules in the water return to the positive plates.

Fully charged and fully discharged states are the extremes. Normally, a battery is partially charged or partially discharged. For example, a battery may be 25% discharged, meaning that 25% of the chemical reaction has taken place and 75% of the battery is in its original chemical condition.

2.2--The Primary Causes of Battery System Malfunction

Before dealing with preventive maintenance and diagnostic procedures for the battery system, we're going to cover certain environmental and usage handling factors that can cause the system to malfunction.

Excessive heat. When batteries are subjected to high temperatures, positive plates corrode quickly and battery cells dry out.

Cold weather. Because engine oil thickens in cold temperatures, it makes engines harder to crank. This places a heavier and longer-lasting drain on the battery.

Vibration. If a battery is not securely fastened to the vehicles frame, the resulting vibration can shed the active material from the battery’s plate grids.

Fast charging. Using a high charging rate to quickly charge batteries can be damaging, if the battery becomes overheated and begins gassing.

Deep cycling. Repeated deep cycling will eventually cause a battery to lose its ability to accept a charge. If battery cycling occurs use high cycle batteries.

2.3--Preventive Maintenance Procedure

There are six preventive maintenance procedures that can help preserve battery life. These six procedures are also the first steps you should take when diagnosing (i.e. troubleshooting) a problem in the vehicle’s electrical system. The six preventive maintenance procedures are as follows:

1. Check cleanliness. If the battery rack is dirty, remove the battery cables first, then remove the battery from the vehicle. Wash the battery rack with a water and baking soda solution. Flush the case with water, and dry with a towel. If necessary, clean the battery post and cable terminal with a wire brush or a special terminal cleaning tool. Wash batteries with baking soda and water.

Figure 6: Battery hold-down brackets.

2. Check hold-down brackets. Make sure the brackets holding the battery to the vehicle’s frame are secure. If the brackets are loose, tighten to manufacturer specifications.

Figure 7: Battery terminal locations.

3. Check battery cables. Battery cable connections to terminal should be checked for corrosion and proper tightness, and cleaned and /or tightened as necessary. The cables themselves should be checked for swelling, cracking, or brittleness, cables should be replaced as necessary.

4. Check battery ground cables. The battery ground cables must be securely fastened to the alternator ground. Also be sure that the points where the cables are connected to the vehicle’s frame or engine block are clean and secure.

5. Check battery case. The condition of the battery case often indicates whether internal component damage or loss has occurred. Telltale signs are swelling and cracking of the case.

6. Check fluid levels (only on non-maintenance-free types of batteries). If liquid in the battery is low, add clean soft water or distilled water only. Adding a premixed electrolyte solution will make the sulfuric acid too strong and cause the plates, separators, and case to deteriorate prematurely.

2.4--Diagnostic / Troubleshooting Procedures

When trying to find the cause of a problem in a vehicle’s electrical system, you should always begin with the battery. In performing any diagnostic procedure, refer to the safety information section in the Introduction section 1.6.

It's critically important for each individual battery to be properly tested and fully charged. It's only then that you can move on to diagnosing problems with the charging or starting systems. A battery not fully charged will cause all other electrical systems tests to be inaccurate.

Remember to always disconnect all battery ground cables, at the batteries, before replacing or servicing any electrical equipment. After removing battery ground cables verify no voltage is present at alternator output terminals.

Beyond the visual inspection procedures mentioned earlier, there are three simple steps to testing a battery: removal of the surface charge, determination of the state of charge, and load testing.

Remove the battery’s surface charge. Electrical charges on the surface of the battery’s positive plates cause a falsely high voltmeter reading. Removal of this so-called “surface charge” is required on batteries that have been charged by an alternator or a battery charger within 48 hours. Batteries on trucks that have not been run or charged on a charger within 48 hours will not have significant surface charge.

To remove the surface charge, you'll need to slightly discharge the batteries. This can be done by using a carbon pile load tester to load each battery to one quarter of its cold cranking amps rating for 15 seconds, see Figure 8. Fifteen seconds is long enough to dissipate the surface charge from the plates.

The surface charge can be removed by simply turning on the vehicle’s lights - without starting the engine - for two to three minutes per battery.

Figure 8: Carbon pile load tester

Test the battery’s state of charge. The second step in battery testing involves testing each individual battery’s state of charge. Connect a voltmeter across each battery and record the readings. Compare the readings to the Figure 9 chart to determine the percentage of charge. If the battery is at 75% or higher, you can proceed to the third step - the load test. If the battery is below 75%, recharge it. (See charging instructions at the end of this section). Remove the surface charge, and then test it again to determine the state of charge. If after recharging the battery, it is still below 75% charged, the battery may require further charging or it may be unserviceable.

Percentage of Charge
12.60 V 100%
12.45 V 75%
12.30 V 50%
12.15 V 25%

Figure 9: Percent of Charge Table

Carbon pile load testing. The third step in battery testing is to load test the battery. Follow the carbon pile load tester manufacturers instructions when connecting the tester and ammeter across the battery. Determine the battery’s cold cranking amp rating, or CCA. Divide the CCA rating by two to determine the load. Load the battery for 15 seconds, adjusting the carbon pile to maintain the proper load. Do not load the battery any longer than 15 seconds, as this may cause damage to the carbon pile. At the end of the 15- second load, read the voltmeter and turn off the carbon pile.

The table in Figure 10 below is used as a guideline for the minimum acceptable load test results. Notice that as the electrolyte temperature declines, so does the minimum voltage. This is due to the effect of temperature on most chemical reactions. The battery reaction is slower as the electrolyte becomes colder.

Minimum Acceptable Results
Electrolyte Temp (F) Voltage
70° or above 9.6
60° 9.5
50° 9.4
40° 9.3
30° 9.1
20° 8.9
10° 8.7

Figure 10: Minimum Acceptable Load Test Results

Batteries that pass the load test may be put back into service. Fully charged batteries that fail the load test have lost capacity or the ability to provide electrical current for cranking.

2.5--Battery Charging

When recharging batteries, please follow these important safety precautions:
  1. Leave the battery charger unplugged until its cables are connected to the battery.
  2. Charge each battery separately.
  3. Use the proper charger.
  4. Charge batteries in a well ventilated area.
  5. Never smoke while charging batteries.
  6. Use protective eye wear.
  7. Do not wear watches or other jewelry.
2.6--Battery Replacement

If you perform regular preventive maintenance on batteries, and always properly charge and test batteries, you can avoid or reduce the need for costly replacements.

However, if your diagnostic procedures point to a faulty battery, you'll need to carefully select a new battery. The new battery’s “cold cranking amp” rating must support the vehicle’s intended application, or load and duty cycle.

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