Absorbent Glass Mat (AGM) Starter Battery
ABSORBENT GLASS MAT (AGM) STARTER BATTERY CHARGING
WARNING: Never exceed 14.4 volts when charging the Absorbent Glass Mat (AGM) starter battery. Personal injury and/or battery damage may result.
Vehicles equipped with the AGM starter battery utilize a unique absorbent glass mat battery design. This battery has a maximum charging voltage that must not be exceeded in order to restore the battery to its full potential, failure to use the following AGM battery charging procedure could result in damage to the battery or personal injury.
Battery charging is the means by which the battery can be restored to its full voltage potential. A battery is fully-charged when:
- OTC One Step Battery Analyzer and Charger special tool number OT-3641 or equivalent tester indicates battery is OK.
- Open-circuit voltage of the battery is 12.65 volts or above.
- Battery passes Load Test multiple times.
WARNING: If the battery shows signs of freezing, leaking, loose posts or low electrolyte level, do not test, assist-boost, or charge. The battery may arc internally and explode. Personal injury and/or vehicle damage may result.
WARNING: Explosive hydrogen gas forms in and around the battery. Do not smoke, use flame, or create sparks near the battery. Personal injury and/or vehicle damage may result.
WARNING: The battery contains corrosive materials. Avoid contact with the skin, eyes, or clothing. In the event of contact, flush with water and call a physician immediately. Keep out of the reach of children.
CAUTION: Always disconnect and isolate the battery negative cable before charging a battery. Charge the battery directly at the battery terminals. Do not exceed 14.4 volts while charging a battery.
CAUTION: The battery should not be hot to the touch. If the battery feels hot to the touch, turn off the charger and let the battery cool before continuing the charging operation. Damage to the battery may result.
After the battery has been charged to 12.6 volts or greater, perform a load test to determine the battery cranking capacity. If the battery passes a load test, return the battery to service. If the battery fails a load test, it is faulty and must be replaced.
Clean and inspect the battery hold downs, well, terminals, posts, and top before completing battery service.
CHARGING A COMPLETELY DISCHARGED BATTERY
WARNING: Never exceed 14.4 volts when charging the Absorbent Glass Mat (AGM) starter battery. Personal injury and/or battery damage may result.
The following procedure should be used to recharge a completely discharged battery. Unless this procedure is properly followed, a good battery may be needlessly replaced.
1. Measure the voltage at the battery posts with a voltmeter, accurate to 1/10 (0.10) volt. Refer to Battery Removal and Installation for access instructions. If the reading is below ten volts, the battery charging current will be low. It could take several hours before the battery accepts a current greater than a few milliamperes. Such low current may not be detectable on the ammeters built into many battery chargers.
2. Disconnect and isolate the battery negative cable. Connect the OTC One Step Battery Analyzer and Charger special tool number OT-3641 or equivalent.
NOTE: Some battery chargers are equipped with polarity-sensing circuitry. This circuitry protects the battery charger and the battery from being damaged if they are improperly connected. If the battery state-of-charge is too low for the polarity-sensing circuitry to detect, the battery charger will not operate. This makes it appear that the battery will not accept charging current. See the instructions provided by the manufacturer of the battery charger for details on how to bypass the polarity-sensing circuitry.
3. Battery chargers vary in the amount of voltage and current they provide. The amount of time required for a battery to accept measurable charging current at various voltages is shown in the Charge Rate Table. If the charging current is still not measurable at the end of the charging time, the battery is faulty and must be replaced. If the charging current is measurable during the charging time, the battery may be good and the charging should be completed in the normal manner.
CHARGING TIME REQUIRED
The time required to charge a battery will vary, depending upon the following factors:
- Battery Capacity - A completely discharged heavy-duty battery requires twice the charging time of a small capacity battery.
- 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 battery charger is connected to a cold battery, the current accepted by the battery will be very low at first. As the battery warms, it will accept a higher charging current rate (amperage).
- Charger Capacity - A battery charger that supplies only five amperes will require a longer charging time. A battery charger that supplies eight amperes will require a shorter charging time.
- State-Of-Charge - A completely discharged battery requires more charging time than a partially discharged battery. Electrolyte is nearly pure water in a completely discharged battery. At first, the charging current (amperage) will be low. As the battery charges, the specific gravity of the electrolyte will gradually rise.
The Battery Charging Time Table gives an indication of the time required to charge a typical battery at room temperature based upon the battery state-of-charge and the charger capacity.
