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 the battery terminals with an accurate voltmeter. If below 11 volts, the charge current will he very low and it could take some time before it accepts a current in excess of a few milliamps. Such low current may be detectable on ammeter available in the field.
2. Set battery charger on high setting.
3. Some chargers feature polarity protection circuitry which prevents charging unless the battery charger leads are connected to the battery terminals correctly. A completely discharged battery may not have enough voltage to activate this circuitry even though battery charger 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 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:
- If the charge current is still not measurable 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 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 (RC) rating of the battery as the number of Ampere Hours of charge will usually bring the green dot into view. For reserve capacity refer to "Application and ID". Application and ID If battery is rated at 75 RC minutes, it would usually be completely recharged as follows:
- 10 ampere charge - 7 1/2 hours - 75 AH.
- 25 ampere charge - 3 hours - 75 AH, etc.
6. It is recommended that any battery recharged by this procedure be LOAD TESTED to establish serviceability. Refer to "Battery Testing". Testing and Inspection