The following procedure should be used to recharge a very low or completely discharged battery. Unless the procedure is followed correctly, a perfectly good battery may be needlessly replaced.

1. Measure the voltage at the battery terminals with an accurate voltmeter. If below 11 volts, the charge current will be very low and it could take some time before it accepts a current in excess of a few milliamps. Such low current may not be detectable on ammeters available in the field.
2. Set the battery charger on a 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 though 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.

Important: 

•	If the charge current IS NOT measurable at the end of the charging times (below), the battery should be replaced.

•	If the charge current IS measurable during the charging time, the battery is considered to be good an charging should be completed in the normal manner.

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

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 rule of thumb, use battery's Reserve Capacity Rating to determine how long it will take to completely recharge the battery. For capacity ratings, refer to Battery Usage . 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 10 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. It is recommended that any battery recharged by this procedure be LOAD TESTED to establish serviceability. Refer to Battery Load Test .