Charging A Completely Discharged Battery

NOTE: Do not use "boost", "jump start", "crank" or equivalent setting for prolonged charging of batteries. Undesirable and potentially dangerous spewing of gasses or electrolyte through the vent hole may occur.

Use the following procedure to charge a completely discharged battery. If the procedure is not followed properly, a good battery may be replaced needlessly.
1. Measure the voltage at the battery terminals. If less than 11 volts, the initial charging current will be very low, and it could take some time before the battery accepts more than a few milliamps of current. Such low current may not be detectable on charge ammeters available in the field.
2. Set the battery charger on high.
3. Some chargers have polarity protection circuitry which prevents charging unless the charger leads are properly connected to the battery. If a battery is very low or completely discharged, it may not have enough voltage to activate the circuitry (even though the leads are properly connected), and it may appear the battery will not accept charging current. If this happens, follow the charger manufacturer's instructions on how to bypass or override the circuitry so the charger will turn on and charge the battery.
4. Battery chargers vary in the amount of voltage and current provided. The time it takes for the battery to accept a measurable current from the charger will vary. It is dependent on how deeply discharged the battery was and the strength of the charging equipment. A charger of less than 14 volts could take up to 16 hours before it appears to be accepting current, followed up by several hours of actual charging time.
5. A completely discharged battery must be charged for a sufficient number of Ampere-Hours (AH) to restore it to a usable state. A general estimate would be to use the reserve capacity rating of the battery, refer to "Specifications", as the number of ampere-hours of charge needed for a deeply discharged battery to have a green "eye" appear. To determine the amount of hours the battery may need to be left on the charger, the following simple calculation can be made:
A. After the meter on the charger starts to show current flow, read the number of amperes being accepted.
B. Divide the reserve capacity of the battery, refer to "Specifications", by the number of amperes shown on the meter.
C. As charging progresses, use the average current flow and the total hours on charge to determine the total ampere-hours.
6. Monitor battery at least hourly. If the battery temperature exceeds 52°C (125°F), as judged by feel, or the electrolyte is spewing from the vents, discontinue charging or reduce the charging rate. When the green dot appears in the hydrometer, discontinue charging. If the green dot has not appeared after twice the charging time calculated above, replace the battery.
7. After charging a battery, load test the battery to be sure the battery is good. If the battery is shorted internally, the voltage will drop over time. A battery may occasionally pass a load test and fail later from the internal short. The best procedure is to wait and re-test the battery again in an hour.