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GM/Detroit 6.5L – 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 J 39200 digital multimeter. If voltage is below 11 volts, charge current will be very low and it could take some time before it accepts current in excess of a few milliamperes.
2. Set the battery charger on the high setting.
3. Some chargers feature polarity protection circuitry that 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 the leads are connected properly, making it appear that the battery will not accept charging current. There­fore, follow the specific charger manufacturer’s instructions telling how to bypass or override the circuitry so 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:
• 16.0 volts or more up to 4 hours
• 14.0 to 15.9 volts up to 8 hours
• 13.9 volts or less up to 16 hours

Important
• If the charge current is not measurable at the end of the above charging times, replace the battery.
• If the charge current is measurable during the charging time, the battery is considered to be good. Complete the charging in the normal manner.

5. It is critical to remember that a completely dis­charged battery must be recharged for a sufficient number of ampere hours (AH) to restore it to a useable state. As a rule of thumb, use the reserve capacity rating of the battery to determine how long it will take to completely recharge the battery. For capacity ratings, refer to “Specifications.” Divide the reserve capacity rating by the amount of ampere charge to determine how many hours of charging are needed. (Rating divided by amps = hours.)
• For example: a battery with a reserve capacity rating of 75, charged at a rate of TO amperes, will take 7.5 hours to fully recharge (75 divided by 10 = 7.5). The same battery, charged at a rate of 25 amperes, will take 3 hours to fully recharge (75 divided by 25 = 3).
6. Any battery recharged by this procedure should be load tested to determine serviceability. Refer to “Di­agnosis of the Battery.”

 

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