Charging A Completely Discharged Battery

The following procedure should be used to recharge a completely discharged battery. Unless the procedure is properly followed, a perfectly good battery may be needlessly replaced.
1. Measure voltage at battery terminals with an accurate voltmeter. When below 11 volts, the charge current is very low and it can take some time before it accepts current in excess of a few milliamperes. Such low current may not be detectable on charger ammeters available in the field.
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 when the leads are connected properly. This makes 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 turns on and charges a low-voltage battery.
4. When the charge current is still not measurable at the end of the following charging times, the battery should be replaced. When 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. use the battery's reserve capacity (RC) rating as the number of AH of charge needed to bring the green dot into view. For example, when the battery is rated at 75 AH minutes. it would be completely recharged as follows: 10 ampere charge x 7-1/2 hours = 75 AH. or 25 ampere charge x 3 hours = 75 AH, etc.
6. It is recommended that any battery recharged by this procedure be LOAD TESTED to establish serviceability.