Battery: Description and Operation
OVERVIEWThe battery, starting, and charging systems operate with one another, and must be tested as a complete system. In order for the vehicle to start and charge properly, all of the components involved in these systems must perform within specifications.
Remember these systems are link together while testing. The diagnostic procedures used include from conventional diagnostic procedures to the more sophisticated On-Board Diagnostics (OBD) built into the Powertrain Control Module (PCM).
The following specialized equipment is needed to perform all the tests in Battery:
- Battery Charger (min. 0-20 amp rated)
- Digital Multi Meter (capable of reading 400 milliamps)
- Hydrometer ('Except on Maintenance-Free batteries)
- Volt/Ammeter/Load Tester
The PCM controls the charging system. Its OBD capabilities monitor or specific charging system functions for faults. If a fault occurs, a Diagnostic Trouble Code (DTC) is set in its memory. Fault codes and their retrieval are covered in Charging System.
INTRODUCTION
The current Model Year batteries are listed in the Battery Specifications Chart. Use this chart to determine:
- Application for vehicle testing
- Maintenance-free or low-maintenance type
- Test Specifications
- Ratings and BCI Group Number
Determine the correct battery for the vehicle before testing.
From the factory, most vehicles are equipped with a maintenance-free battery, and others with a low-maintenance battery. A Hydrometer test may be required for low-maintenance batteries that is not required on maintenance-free (sealed) batteries.
NOTE: Vehicles using a Maintenance-Free battery, should be replaced with a Maintenance-Free battery.
Maintenance Free Battery:
Maintenance-free batteries have non-removable battery vent caps. Water cannot be added to this battery. Under normal service the composition of this battery reduces gassing and water loss at normal charge rates. If the battery electrolyte level becomes low, this battery must be replaced.
Low Maintenance Battery:
Low-maintenance batteries have removable battery cell caps . Water can be added to this battery Under normal service the composition of this battery reduces gassing and water loss at normal charge rates.
Rapid loss of electrolyte can be caused by an over charging condition. Be certain to diagnose the charging system before returning the vehicle to service.
It is important that the battery, starting and charging systems be thoroughly tested and inspected any time a battery needs to be charged or replaced. The cause of abnormal discharge, over charging or early battery failure must be corrected before a battery is replaced or returned to service.
The battery must be fully charged before any tests can be performed.
SYSTEM OPERATION
Battery
The battery has three major electrical system functions: First, it provides an energy source for cranking the engine; second, it acts as an electrical system voltage stabilizer; third, it delivers electrical current to operate various electrical systems in the vehicle, for a limited time, when the electrical load exceeds the generator output or during engine off conditions.
The battery is a device used to store electrical energy potential in a chemical form. When an electrical load is applied to the battery terminals, an electrochemical reaction occurs within the battery. This reaction causes the battery to discharge electrical current.
The battery is made up of six individual cells that are connected in series. Each cell contains positive charged plate groups made of lead oxide, and negatively charged plate groups made of sponge lead. The dissimilar metal plates are submerged in a sulfuric acid and water solution called an electrolyte.
As the battery discharges, a gradual chemical change takes place within each cell. The sulfuric acid in the electrolyte combines with the plate material causing both plates to slowly change to lead sulfate. At the same time, oxygen from the positive plate material combines with hydrogen from the sulfuric acid, causing the electrolyte to become mainly water.
The chemical changes within the battery are caused by the movement of excess or free electrons between the positive and negative plate groups. This movement of electrons produces a flow of electrical current through the load device attached to the battery terminals. As the plate materials become more similar chemically and the electrolyte becomes less acid, the voltage potential of each cell is reduced. However, by charging the battery with a voltage higher than that of the battery, the battery discharging process is reversed.
Charging the battery gradually changes the sulfated lead plates back into sponge lead and lead oxide, and the water back into sulfuric acid. This action restores the difference in the electron charges deposited on the plates, and the voltage potential of the battery cells.
For a battery to remain useful, it must be able to produce high-amperage current over an extend period. A battery must also be able to accept a charge so that its voltage potential may be restored.
In addition to producing and storing electrical energy, the battery serves as a capacitor, or voltage stabilizer, for a vehicle's electrical system. It absorbs most abnormal or transient voltages caused by the switching of any of the vehicle's electrical components
The battery is vented to release excess hydrogen gas that is created when the battery is being charged or discharged. However, even with these vents, the hydrogen gas can collect in or around the battery. hydrogen gas is exposed to flame or sparks it might ignite.
If the electrolyte level is low, the battery may arc internally and explode. If the battery is equipped with removable cell caps, add distilled water when-ever the electrolyte level is below the top of the plates. If the battery cell caps cannot be removed, the battery must be replaced if the electrolyte level becomes low.
Battery Ignition Off Draw (IOD)
A completely normal vehicle will have a small amount of current drain on the battery with the key out of the ignition. It can range from 5 to 25 milliamperes after all the modules time out. If a vehicle will not be operated for approximately a 20 days, the IOD fuse should be pulled to eliminate the vehicle electrical drain on the battery during storage. The IOD fuse (M1) is located in the junction Block. Refer to the raised fuse or the cover of the Junction Block for proper fuse.
Charging Time Required
The time required to charge a battery will vary depending upon the following factors.
Battery Charging Timetable Chart:
Size Of Battery
A completely discharged large heavy-duty battery may require more recharging time than a completely discharged small capacity battery. Refer to Battery Charging Timetable.
WARNING
- NEVER EXCEED 20 AMPS WHEN CHARGING A COLD -1°C (30°F) BATTERY. THE BATTERY MAY ARC INTERNALLY AND EXPLODE. PERSONAL INJURY AND/OR VEHICLE DAMAGE MAY RESULT.
- DO NOT CHARGE, ASSIST BOOST, LOAD TEST, OR ADD WATER TO THE BATTERY WHEN CLEAR COLOR DOT IS VISIBLE, PERSONAL INJURY MAY OCCUR.
Test Indicator:
A clear color dot shows electrolyte level in the battery is below the test indicator. Water cannot be added to a maintenance free battery. The battery must be replaced. A low electrolyte level may be caused by an over charging condition. Refer Generator System for test procedures.
Temperature
A longer time will be needed to charge a battery at -18°C (0°F) than at 27°C (80°F). When a fast charger is connected to a cold battery, current accepted by battery will be very low at first. In time, the battery will accept a higher rate as battery temperature warms.
Charger Capacity
A charger which can supply only five amperes will require a much longer period of charging than a charger that can supply 20 amperes or more.
State Of Charge
A completely discharged battery requires more charging time than a partially charged battery. Electrolyte is nearly pure water in a completely discharged battery. At first, the charging current amperage will be low. As water is converted back to sulfuric acid inside the battery, the current amp rate will rise. Also, the specific gravity of the electrolyte will rise, bringing the green ball into view at approximately 75 percent state-of-charge.