Battery: Description and Operation

INTRODUCTION
The battery stores, stabilizes, and delivers electrical current to operate various electrical systems in the vehicle. The determination of whether a battery is good or bad is made by its ability to accept a charge. It also must supply high-amperage current for a long enough period to be able to start the vehicle. The capability of the battery to store electrical current comes from a chemical reaction. This reaction takes place between the sulfuric acid solution (electrolyte) and the lead +/- plates in each cell of the battery. As the battery discharges, the plates react with the acid from the electrolyte. When the charging system charges the battery, the water is converted to sulfuric acid in the battery. The concentration of acid in the electrolyte is measured as specific gravity using a hydrometer. The original equipment (OE) battery is equipped with a hydrometer (test indicator) built into the battery cover. The specific gravity indicates the battery's state-of-charge. The OE battery is sealed and water cannot be added.

The battery is vented to release gases that are created when the battery is being charged and discharged. The battery top, posts, and terminals should be cleaned when other under hood maintenance is performed.

When the electrolyte level is below the top of the plates, Clear in the test Indicator, the battery must be replaced. The battery must be completely charged, and the battery top, posts, and cable clamps must be cleaned before diagnostic procedures are performed.

SYSTEM OPERATION

Battery Heat Shield (Thermoguard)
A plastic bubble-wrap style thermoguard slides over the battery case to enclose the sides of the battery. The thermoguard protects the battery from engine compartment temperature extremes.

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 milliampere 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 The IOD fuse is located in the Power Distribution Center (PDC). Refer to the PDC cover for proper fuse.

Charging Time Required

WARNING: NEVER EXCEED 20 AMPS WHEN CHARGING A COLD -1 °C (30 °F) BATTERY. PERSONAL INJURY MAY RESULT.

The time required to charge a battery will vary depending upon the following factors.

Size Of Battery

Battery Charging Timetable:

A completely discharged large heavy-duty battery may require more recharging time than a completely discharged small capacity battery, refer to the Battery Charging Timetable for charging times.

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

Built-In Test Indicator Sight Glass:

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.

BATTERY PROTECTION

Park & Headlamps
This feature provides a battery protection scheme to avoid wearing down the battery if the customer leaves the parklamps or headlamps on for extended periods of time with the ignition OFF. If the parklamp or headlamp switch remains in the active position for more than 3 minutes, while the ignition is OFF, the parklamps and or headlamps will be turned off and the input causing the lamps to be on will be ignored. Once the 3 minute timeout has elapsed, the BCM will enter sleep mode. Any change in any inputs monitored by the BCM that brings the BCM out of sleep mode, will reset the 3 minute timer (door lock/unlock), door ajar, ignition, RKE actuation, etc.).

Leaving the ignition switch in an active position (steering column unlocked, ignition ON or accessory power ON) will inhibit the battery protection routine from turning off the exterior lamps as described above.

Reading & Glove Box Lamps
This feature provides a battery protection scheme to avoid wearing down the battery due to leaving a reading lamp on, glove box open or visor vanity mirrors on. The BCM provides a ground circuit for these interior lamps. This ground path is connected whenever the ignition is ON but is always disconnected 15 minutes after the BCM enters sleep mode. Once the 15 minutes timeout has expired, any monitored input that brings the BCM out of sleep mode (ignition/unlock switch, door ajar switches, dome lamp switch, RKE/Central Unlock actuation etc.) will reset the 15 minute timer and return the reading, glove box lamps and vanity mirrors to normal operation (normal operation defined as: "ON" is reading lamp and visor vanity mirrors ON, or glove box open; "OFF" is reading lamp and visor vanity mirrors OFF, and glove box closed).

Leaving the keys in the ignition switch, while the ignition is OFF, will not inhibit the battery protection from turning off these interior lamps as described above. Leaving the ignition switch in an active position (steering column unlocked, ignition ON or accessory power on) will inhibit the battery protection routine from turning off these interior lamps as described above.