Lead Acid Batteries and Jump Starts

This topic will cover basic battery operation, maintenance and testing. Batteries are very dangerous devices for several reasons. If you are not qualified to work with batteries, then we suggest you have a professional do it for you.

Battery Safety Issues

Safety is always an important consideration while working with batteries. Remove all of your jewelry, so that you won't melt your watch band or ring while you are working. It is one thing to ruin your ring, but quite another thing to try and remove a red hot ring from your burning finger. Because gold is a perfect conductor, that innocent ring or watch band will heat up much faster than you ever thought possible.

The hydrogen gas produced by charging or discharging batteries is very explosive. I have seen three batteries blow up and trust me, it is not a pretty sight. This is a good time to use those safety goggles that are hanging on the wall. Sulfuric acid eats up clothing, so you may want to consider wearing junk clothing while working with batteries.

When doing work on electrical circuits in vehicles, it is best to disconnect the ground cable. Just remember you are playing around with corrosive acid, explosive gases and hundreds of amps of electrical current capacity which has welding capabilities.

Battery Stored Energy

Batteries provide a way to store electrical energy in chemical form. When electrical energy is required, the battery converts chemical energy into electrical energy as needed. The lead acid battery, is composed of lead plates and acid electrolyte, and is used for all truck applications.

Each truck battery cell produces 2 volts; therefore 12-volt batteries have 6 cells. The two plates of the battery cell are labeled plus (+) and minus (-). As the lead acid battery is charged, the charging energy is stored within the electrolyte (acid) of the battery, and a 2-volt potential difference exists between the two battery plates. When the battery is in use (or discharged), the electrolyte and the battery plates work together to provide free electrons to do the battery's work. In other words, the energy stored within the battery is converted chemically into electron potential difference between the two plates, which performs electrical work outside of the battery.

Battery Ratings

Battery rating is based upon the number of plates per cell and the total surface area of each plate. Given the number of plates and surface area, then the strength and volume of electrolyte also determine the battery output. The temperature of the battery also dictates the battery output. During extreme cold weather, the battery has less output capability.

The battery reserve capacity represents the number of minutes that the battery can produce 25 amps. This is an approximation of night driving without a working alternator.

The cold cranking test measures the minimum cranking amps available at zero degrees. This measurement specifies the number of cranking amps maintained for 30 seconds while the battery terminal voltage remains above 7.2 volts (12 volt battery). The cold cranking power for a truck starter is about 1 amp for each cubic-inch of engine displacement. As an example, the Caterpillar 3406E has 893 cu-in displacement. Therefore the cold cranking rating of the battery should be about 900 amps.

A battery at -20 degrees will produce about 20% of its rated cranking current, and a battery at 32 degrees will produce about 50% of the output that the same battery would produce at 80 degrees. It is also important to note that a very cold engine requires about 2.5 times the cranking power of a warm engine.

Battery Maintenance

Battery Maintenance is an important issue. The battery should be clean. Use a baking soda and water mix to clean the battery. Cable connections need to be clean and tight. Many battery problems are caused by dirty and loose connections. Serviceable batteries need to have their fluid levels checked. Use only mineral free water, distilled water is best. Don't overfill the battery cells especially in warmer weather. The natural fluid expansion in hot weather will push excess electrolytes from the battery. Add distilled water to the level indicated by the battery manufacturer or to 1/8" BELOW the bottom of the filler tube (vent wells).

To prevent corrosion of cables on top post batteries, use a small bead of silicon sealer at the base of the post and place a felt battery washer over it. Coat the washer with high temperature grease or petroleum jelly (Vaseline). Then place the cable on the post and tighten. Coat the exposed cable end with the same grease. Most truckers don't realize that just the gases from the battery condensing on the metal parts is what causes most cable corrosion.

Battery Operation

Battery current is produced by a chemical reaction between the positive and negative plates, that are submerged in the electrolyte (diluted sulfuric acid). This chemical reaction will cause the battery to self discharge if it is stored unused for a long period of time.

All batteries produce oxygen and hydrogen during charge and discharge. These gases are produced by the breaking apart of water molecules in the electrolyte. As these gases escape, the water level of the battery goes down.

The electrolyte specific gravity of a fully charged battery is 1.260 - 1.270 at 80 degrees. This means that the electrolyte is heavier than water which has 1.000 specific gravity. The electrolyte consists of about 64% water and 36% acid.

During discharge of the battery, oxygen in the positive plate combines with hydrogen in the electrolyte solution, to form water. At the negative plate, lead combines with the sulfate radical to form lead sulfate. Upon complete discharge of the battery, the electrolyte consists of 17% sulfuric acid and 83% water. Since there is now more water and less sulfuric acid, the specific gravity of the electrolyte has decreased to about 1.100

When using a hydrometer, the temperature determines an offset to add to the hydrometer float reading. The hydrometer shown above, incorporates a thermometer chart at the bottom. This consists of a chart which shows the amount to add or subtract from the hydrometer float reading. For example, if the hydrometer reads 1.230 and the temperature is 90 degrees, then add .004 to the reading for a final reading of 1.234. The temperature offset to add or subtract always consists of 0.0xx, not just xx.

Battery Testing

Slow cranking, especially on a cold day, is a good indication that your battery may be going bad and should be tested. An easy way to test a battery is by measurement of the specific gravity, or measurement of the battery voltage. To measure specific gravity, use a temperature compensating hydrometer, which can be found at most auto parts stores for around $5.00. Or you can measure the battery voltage, using a digital D.C. Voltmeter.

If you have a maintenance free wet cell battery, the best way to test is with the voltmeter. Most of the maintenance free batteries have a built in hydrometer that tells you the condition of 1 of the 6 cells. You may get a good reading from 1 cell but have a problem with any one of the other 5 cells in the battery. Therefore the built in one cell hydrometer is not very good indicator of battery condition.

If you have just recharged you battery or driven your truck, eliminate any surface charge before testing, by using one of the following methods;

  • Allow the battery to sit for two to three hours
  • Turn the headlights on high beam for five minutes and then wait five minutes
  • With a battery load tester, apply a load at one half the battery's CCA rating for 15 seconds and then wait five minutes.

After the surface charge has been removed, the following table demonstrates the relationships of battery charge:

Battery Voltage
Specific Gravity
Battery Charge (%)
00% charged
25% charged
50% charged
75% charged
100% charged

Extending Battery Life

Battery life and performance have become shorter as energy requirements increase with the increased electrical load of trucks. It is interesting to note that 80% of all battery failures are related to battery plate sulfation build-up.

This build up occurs when the sulfur molecules in the electrolyte (battery acid) becomes so deeply discharged that they begin to coat the battery lead plates. After time the plates become coated and the battery fails. Here is a list of typical causes of sulfation build-up:

  • Batteries sitting too long between charges. As little as 24 hours in hot weather and several days in cold weather.
  • Battery storage, leaving a battery sit without some type of energy input.
  • Deep cycling the engine start battery, remember these batteries can't handle deep discharge.
  • Undercharging of the battery.
  • Tempertures of 100 plus F. increases battery internal discharge. As the temperature increases, so does the internal discharge. A new and fully charged battery left in 110 degrees F. for 30 days, would not crank over an engine.
  • Low electrolyte level exposes battery plates to air, which will immediately sulfate.
  • Cold weather is hard on the battery because the chemistry does not work well, leaving the battery partially charged, resulting in sulfation.

As a normally battery ages, the active plate material sheds (or flakes off) due to the expansion and contraction that occurs during the discharge and recharge cycles. Deep discharges, heat and vibration, accelerate this aging process. Eventually, the sediment which builds up in the bottom of the cell, can short out that cell.

Parasitic Battery Drain

Parasitic drain is a load put on a battery with the key off. Many vehicles have clock radios, alarm systems, and other electrical loads with the key switched off. You may also have parasitic loads caused by a short in the electrical system. If you are always having dead battery problems most likely the parasitic drain is excessive. The constant low or dead battery caused by excessive parasitic energy drain, will dramatically shorten the battery life. Find the source of excessive parasitic drain and get rid of it if you want prolonged battery life.

Emergency Jump Starting

The following considerations are necessary for safe and successful jump starts. This list of requirements may appear quite lengthy, but failure to recognize these requirements usually results in damage to vehicles and/or people, or failed success. First we will show the usual battery configurations and where the boost cables should be connected. Then we will list the requirements that you should heed for safety's sake.

Emergency Jump Starting Continued

1. In cold weather, a good quality booster cable with four to six gauge wire is necessary to provide enough charging current to the disabled truck. (The smaller the wire gauge number, i.e., the larger the wire diameter, the better.)

2. Ensure that both vehicles are negative ground or positive ground systems. Do not mix system polarities. Mixed polarity systems can cause damage to both trucks.

3. Do not allow the booster cable clamps to touch each other.

4. Do not allow the positive clamp to touch the frame or engine block for negative ground systems.

5. Do not allow the negative clamp to touch the frame or engine block for positive ground systems.

6. If below freezing, look at the electrolyte to determine that the electrolyte is not frozen in the dead battery. If frozen, thaw out the battery before proceeding. A discharged battery, battery voltage or 12.0 volts or less and/or a specific gravity of 1.140 or less, will freeze at approximately 8 degrees F.

7. Without the trucks touching each other, turn off all unnecessary accessories and lights on both trucks, and ensure plenty of ventilation around the batteries, and use protective eye ware.

8. Start the truck with the good battery and let it run for at least two or three minutes at fast idle to recharge it's own battery before proceeding.

9. Connect the positive booster cable clamp (usually RED) to the positive terminal on the dead battery. Connect the positive booster cable clamp on the other end of the booster cable to the positive terminal on the good battery.

10. Connect the negative booster cable clamp (usually BLACK) to the negative terminal on the good battery and the negative booster cable clamp on the other end to a clean, unpainted area on the engine block or frame on the disabled truck, and away from the battery.

11. Let the good truck continue to run at high idle for five minutes or more to allow the dead battery to receive some recharge and to warm it's electrolyte.

12. If the bad truck has two battery banks, which are not in parallel during normal charging, then charge each bank, one at a time, for ten minutes or more. This will also warm up both batteries which makes them more powerful.

13. Start the disabled truck and allow to run at high idle. If the truck does not start the first time, recharge the batteries for another ten minutes (each bank) and try again.

14. Disconnect the booster cables in the reverse order, starting with the negative clamp on the block or frame of the disabled truck to minimize the possibility of a spark near the batteries which could cause a hydrogen gas explosion.

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