Use the following procedure to charge a completely discharged battery. If this procedure is not followed, a good battery may be needlessly replaced.

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

1. Measure the battery voltage at the battery terminals using a digital multimeter:

•	A reading of less than 11 V indicates that the initial charging will be very low.

•	It will take some time before the battery accepts current in excess of a few milliamperes.

2. Set the battery charger on the highest setting.
3. If necessary, disable the polarity protection circuitry:

•	This circuitry, available on most chargers, prevents charging unless the charger leads are properly connected to the battery terminals.

•	A completely discharged battery may not have enough voltage to activate this circuitry, even though the leads are properly connected, implying that the battery will not accept a charge.

•	Most chargers have an override or a bypass function so that the charger will turn ON and charge a low voltage battery. Follow the charger manufacturer's instructions for the override or bypass function.

4. The required battery charge time varies according to the voltage capabilities of the battery charger. A charger of less than 14 V could take up to 16 hours before it appears to be accepting current, followed by several hours of the actual charging time.
5. To determine the amount of hours the battery may need to be charged, perform the following calculation:

•	The reserve capacity rating on the battery label is the number of ampere-hours of charge required in order to produce the green hydrometer dot.

•	After the meter on the charger starts to show current flow, note the number of amperes being accepted.

•	Determine the reserve capacity of the battery. Refer to Battery Usage .

•	Divide the reserve capacity by the number of amperes shown on the meter to determine how many hours of charging is needed.

6. When the green dot appears in the hydrometer, discontinue charging.
7. If the green hydrometer dot is not visible after twice the charging time calculated previously, replace the battery. Refer to Battery Replacement .
8. Monitor the battery 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.
9. Test the battery after charging. Refer to Battery Check .