Jeep Cherokee (XJ): Description and operation

Battery

DESCRIPTION

1 - POSITIVE POST
2 - VENT
3 - CELL CAP
4 - TEST INDICATOR
5 - CELL CAP
6 - VENT
7 - NEGATIVE POST
8 - GREEN BALL
9 - ELECTROLYTE LEVEL
10 - PLATE GROUPS
11 - LOW-MAINTENANCE BATTERY

A large capacity, low-maintenance storage battery (Fig. 1) is standard factory-installed equipment on this model. Male post type terminals made of a soft lead material protrude from the top of the molded plastic battery case to provide the means for connecting the battery to the vehicle electrical system. The battery positive terminal post is visibly larger in diameter than the negative terminal post, for easy identification. The letters POS and NEG are also molded into the top of the battery case adjacent to their respective positive and negative terminal posts for additional identification confirmation. Refer to Battery Cables in the index of this service manual for the location of more information on the battery cables that connect the battery to the vehicle electrical system.

This battery is designed to provide a safe, efficient and reliable means of storing electrical energy in a chemical form. This means of energy storage allows the battery to produce the electrical energy required to operate the engine starting system, as well as to operate many of the other vehicle accessory systems for limited durations while the engine and/or the charging system are not operating. The battery is made up of six individual cells that are connected in series. Each cell contains positively charged plate groups that are connected with lead straps to the positive terminal post, and negatively charged plate groups that are connected with lead straps to the negative terminal post. Each plate consists of a stiff mesh framework or grid coated with lead dioxide (positive plate) or sponge lead (negative plate). Insulators or plate separators made of a non-conductive material are inserted between the positive and negative plates to prevent them from contacting or shorting against one another. These dissimilar metal plates are submerged in a sulfuric acid and water solution called an electrolyte.

The factory-installed battery has a built-in test indicator (hydrometer). The color visible in the sight glass of the indicator will reveal the battery condition.

For more information on the use of the built-in test indicator, refer to Battery in the index of this service manual for the location of the proper battery diagnosis and testing procedures. The factory-installed low-maintenance battery has removable battery cell caps. Water can be added to this battery.

The battery is not sealed and has vent holes in the cell caps. The chemical composition of the metal coated plates within the low-maintenance battery reduces battery gassing and water loss, at normal charge and discharge rates. Therefore, the battery should not require additional water in normal service.

If the electrolyte level in this battery does become low, water must be added. However, rapid loss of electrolyte can be caused by an overcharging condition. Be certain to diagnose the charging system after replenishing the water in the battery for a low electrolyte condition and before returning the vehicle to service. Refer to Charging System in the index of this service manual for the location of the proper charging system diagnosis and testing procedures.

For battery maintenance schedules and jump starting procedures, see the owner's manual in the vehicle glove box. Optionally, refer to Maintenance Schedules and Jump Starting, Towing and Hoisting in the index of this service manual for the location of the recommended battery maintenance schedules and the proper battery jump starting procedures. While battery charging can be considered a maintenance procedure, the battery charging procedures and information are located in the service procedures section of this service manual. This was done because the battery must be fully-charged before any battery diagnosis or testing procedures can be performed.

Refer to Battery Charging in the index of this service manual for the location of the proper battery charging procedures.

NOTE: This group covers both Left-Hand Drive (LHD) and Right-Hand Drive (RHD) versions of this model. Whenever required and feasible, the RHD versions of affected vehicle components have been constructed as mirror-image of the LHD versions.

While most of the illustrations used in this group represent only the LHD version, the diagnostic and service procedures outlined can generally be applied to either version. Exceptions to this rule have been clearly identified as LHD or RHD, if a special illustration or procedure is required.

BATTERY SIZE AND RATINGS

The battery Group Size number, the Cold Cranking Amperage (CCA) rating, and the Reserve Capacity (RC) rating or Ampere-Hours (AH) rating can be found on the original equipment battery label. Be certain that a replacement battery has the correct Group Size number, as well as CCA, and RC or AH ratings that equal or exceed the original equipment specification for the vehicle being serviced. Refer to Battery in the index of this service manual for the location of the proper factory-installed battery specifications.

Battery sizes and ratings are discussed in more detail below.

•  Group Size
  The outside dimensions and terminal placement of the battery conform to standards established by the Battery Council International (BCI). Each battery is assigned a BCI Group Size number to help identify a correctly-sized replacement.
•  Cold Cranking Amperage
  The Cold Cranking Amperage (CCA) rating specifies how much current (in amperes) the battery can deliver for thirty seconds at -18 C (0 F). Terminal voltage must not fall below 7.2 volts during or after the thirty second discharge period. The CCA required is generally higher as engine displacement increases, depending also upon the starter current draw requirements.
•  Reserve Capacity
  The Reserve Capacity (RC) rating specifies the time (in minutes) it takes for battery terminal voltage to fall below 10.5 volts, at a discharge rate of 25 amperes. RC is determined with the battery fullycharged at 26.7 C (80 F). This rating estimates how long the battery might last after a charging system failure, under minimum electrical load.
•  Ampere-Hours
  The Ampere-Hours (AH) rating specifies the current (in amperes) that a battery can deliver steadily for twenty hours, with the voltage in the battery not falling below 10.5 volts. This rating is also sometimes identified as the twenty-hour discharge rating.

OPERATION

When an electrical load is applied to the terminals of the battery, an electrochemical reaction occurs.

This reaction causes the battery to discharge electrical current from its terminals. As the battery discharges, a gradual chemical change takes place within each cell. The sulfuric acid in the electrolyte combines with the plate materials, 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 itself, the battery discharging process is reversed. Charging the battery gradually changes the sulfated lead plates back into sponge lead and lead dioxide, 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 extended period. A battery must also be able to accept a charge, so that its voltage potential may be restored.

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, hydrogen gas can collect in or around the battery. If hydrogen gas is exposed to flame or sparks, it may 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 whenever 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.

In addition to producing and storing electrical energy, the battery serves as a capacitor and voltage stabilizer for the electrical system of the vehicle. It absorbs most abnormal or transient voltages caused by the switching of any of the electrical components in the vehicle.

Battery cables

DESCRIPTION

The battery cables (Fig. 2) are large gauge, stranded copper wires sheathed within a heavy plastic or synthetic rubber insulating jacket. The wire used in the battery cables combines excellent flexibility and reliability with high electrical current carrying capacity. Refer to Wiring Diagrams in the index of this service manual for the location of the proper battery cable wire gauge information.

A clamping type female battery terminal made of soft lead is die cast onto one end of the battery cable wire. A square headed pinch-bolt and hex nut are installed at the open end of the female battery terminal clamp. Large eyelet type terminals are crimped onto the opposite end of the battery cable wire and then solder-dipped. The battery positive cable wires have a red insulating jacket to provide visual identification and features a larger female battery terminal clamp to allow connection to the larger battery positive terminal post. The battery negative cable wires have a black insulating jacket and a smaller female battery terminal clamp.

The battery cables cannot be repaired and, if damaged or faulty they must be replaced. Both the battery positive and negative cables are available for service replacement only as a unit with the battery wire harness, which may include portions of the wiring circuits for the generator and other components on some models. Refer to Wiring Diagrams in the index of this service manual for the location of more information on the various wiring circuits included in the battery wire harness for the vehicle being serviced.

Fig. 2 Battery Cables

1 - BATTERY
2 - RADIATOR CROSSMEMBER
3 - TERMINAL CLAMPS
4 - FENDER INNER SHIELD
5 - NEGATIVE CABLE
6 - POSITIVE CABLE

OPERATION

The battery cables connect the battery terminal posts to the vehicle electrical system. These cables also provide a return path for electrical current generated by the charging system for restoring the voltage potential of the battery. The female battery terminal clamps on the ends of the battery cable wires provide a strong and reliable connection of the battery cable to the battery terminal posts. The terminal pinch bolts allow the female terminal clamps to be tightened around the male terminal posts on the top of the battery. The eyelet terminals secured to the ends of the battery cable wires opposite the female battery terminal clamps provide secure and reliable connection of the battery to the vehicle electrical system.

The battery positive cable terminal clamp is die cast onto the ends of two wires. One wire has an eyelet terminal that connects the battery positive cable to the B(+) terminal stud of the Power Distribution Center (PDC), and the other wire has an eyelet terminal that connects the battery positive cable to the B(+) terminal stud of the engine starter motor solenoid.

The battery negative cable terminal clamp is also die cast onto the ends of two wires. One wire has an eyelet terminal that connects the battery negative cable to the vehicle powertrain through a stud on the right side of the engine block. The other wire has an eyelet terminal that connects the battery negative cable to the vehicle body through a ground screw on the right front fender inner shield, near the battery.

Battery hold downs

DESCRIPTION

Fig. 3 Battery Hold Downs

1 - SCREW AND WASHER (1)
2 - NUT AND WASHER (2)
3 - T-BOLT (2)
4 - RETAINER (2)
5 - BATTERY TRAY
6 - UPPER RADIATOR CROSS MEMBER
7 - BRACKET
8 - STRAP

The battery hold down hardware (Fig. 3) includes two T-bolts with plastic push-on retainers, a hold down bracket, a stamped steel battery support strap, two hex nuts with coned washers and a single hex screw with a coned washer. The battery hold down bracket consists of a formed steel rod with a stamped steel angle bracket welded to each end. The hold down bracket assembly is then plastic-coated for corrosion protection.

When installing a battery into the battery tray, be certain that the hold down hardware is properly installed and that the fasteners are tightened to the proper specifications. Improper hold down fastener tightness, whether too loose or too tight, can result in damage to the battery, the vehicle or both. Refer to Battery Hold Downs in the index of this service manual for the location of the proper battery hold down installation procedures, including the proper hold down fastener tightness specifications.

OPERATION

The battery hold down hardware secures the battery to the battery tray in the engine compartment.

The hold down support strap provides an additional anchor point for the upper end of the battery and hold down hardware at the upper radiator crossmember.

This hardware is designed to prevent battery movement during vehicle operation. Unrestrained battery movement during vehicle operation can result in damage to the vehicle, the battery or both.

The hold down T-bolts are installed onto the battery tray before the tray is installed in the engine compartment. The T-bolts are inserted through a hole in a molded formation integral to each side of the battery tray from underneath, with the threaded ends of the bolts extending upward. A plastic push-on retainer is installed over each T-bolt to secure the T-bolts to the battery tray for ease of assembly during the vehicle manufacturing process. However, these plastic push-on retainers are not available or required for service replacement.

The battery hold down bracket is installed across the top of the battery case and over the two upright threaded ends of the T-bolts. The round hole in the support strap is then installed over the threaded end of the forward T-bolt and the slotted hole of the strap is secured by a screw with washer to the upper radiator cross member. A hex nut with coned washer is then installed and tightened onto each of the T-bolts to securely hold down the battery in the battery tray.

Battery thermoguard

DESCRIPTION

Fig. 4 Battery Thermoguard

1 - THERMOGUARD
2 - BATTERY

A flexible plastic bubble-wrap style thermoguard (Fig. 4) slides over the battery case to enclose the sides of the battery. The thermoguard consists of a heavy black plastic outer skin and two lighter plies of plastic that have been formed into a sheet with hundreds of small air pockets entrapped between them.

The resulting material is very similar to the bubblewrap used to protect items in many parcel packaging and shipping applications.

OPERATION

The thermoguard protects the battery from engine compartment temperature extremes. The air trapped between the plastic plies of the thermoguard create a dead air space, which helps to insulate the sides of the battery case from the surrounding engine compartment air temperature.

Battery tray

DESCRIPTION

The battery is mounted in a molded plastic tray (Fig. 5) located in the right front corner of the engine compartment. Two T-bolts that are part of the battery hold down hardware are assembled to the battery tray before the tray is installed in the vehicle.

The battery tray is secured by three hex nuts with coned washers to three weld studs located on the front extension of the right front wheelhouse inner panel, forward of the right front wheel.

A hole in the bottom of the battery tray is fitted with a battery temperature sensor. Refer to Battery Temperature Sensor in the index of this service manual for the location of more information on the battery temperature sensor. Refer to Battery Hold Downs in the index of this service manual for the location of more information on the battery hold down hardware.

Fig. 5 Battery Tray

1 - TRAY
2 - NUT AND WASHER (3)
3 - T-BOLT (2)
4 - RETAINER (2)
5 - WELD STUD (3)

OPERATION

The battery tray provides a mounting location and support for the vehicle battery. The battery tray also provides anchor points for the battery hold down hardware. The battery tray and the battery hold down hardware combine to secure and stabilize the battery in the engine compartment, which prevents battery movement during vehicle operation. Unrestrained battery movement during vehicle operation can result in damage to the vehicle, the battery or both.