Charging A Very Low or Completely Discharged Battery
The following procedure should be used to recharge a very low or completely discharged battery:Unless the procedure is properly followed, a perfectly good battery may be needlessly replaced.
1. Measure voltage at battery terminals with a digital voltmeter. If below 10 volts, then the charge current will be very low and it could take some time before it accepts a current in excess of a few milliamperes. Such low current may not be detectable on ammeters used on chargers.
2. Set battery charger-on high setting.
3. Some chargers feature polarity protection circuitry which prevents charging unless the charger leads are connected to the battery terminals correctly. A completely discharged battery may not have enough voltage to activate this circuitry, even though leads are connected properly, making it appear that the battery will not accept charging current. Therefore, follow the specific charger manufacturer's instruction telling how to bypass or override the circuitry so that the charger will turn on and charge a low-voltage battery.
4. Battery chargers vary in the amount of voltage and current they provide. The time required for the battery to accept measurable charger current at various voltages may be as follows:
CHARGER VOLTAGE HOURS
A. 16.0 or more Up to 4 hrs.
B. 14.0 - 15.9 Up to 8 hrs.
C. 13.9 or less Up to 16 hrs.
If the ammeter on the battery charger indicates that the battery is still not accepting a charge at the end of the above charging times, the battery should be replaced.
If the charge current is measurable during the charging time, the battery is considered to be good and charging should be completed in the normal manner.
5. It is important to remember that a completely discharged battery must be recharged for a sufficient number of ampere hours (AH) to restore it to a usable state. As a general rule of thumb, using the reserve capacity rating (RC) (refer to Section 6D of the appropriate service Manual) of the battery as the number of ampere hours of charge will usually bring the green dot into view.
For example, if battery is rated at 75 RC minutes, it would be completely recharged as follows:
10 ampere charge x 7-1/2 hrs. = 75 AH or
25 ampere charge x 3 hrs. = 75 AH, etc.
6. It is recommended that any battery recharged by this procedure be LOAD TESTED to establish serviceability.
RATINGS
A battery has two ratings: (1) a reserve capacity rating at 27 degrees Celsius (80 degrees Fahrenheit) which is the time a fully charged battery will operate the car with no generator operation; and (2) a cold rating at -18 degrees Celsius (0 degrees Fahrenheit) which indicates the cranking load capacity (see battery label or specification chart at the end of the battery section for specific battery ratings.)
RESERVE CAPACITY
The "Reserve Capacity" is the maximum length of time it is possible to travel at night with, minimum electrical load and no generator output.
Expressed in minutes it is the time required for a fully charged battery, at a temperature of 80 degrees Fahrenheit being discharged at a constant current of 25-amperes, to reach a terminal voltage of 10.5 volts.