Tools Required

J 39200 Digital Multimeter

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 the battery voltage at the battery terminals using a J 39200 .

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

•	It could 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.

4. The required battery charge time varies according to the voltage capabilities of the battery charger. 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.
5. To determine the amount of hours the battery may need to be charged, the following calculation can be made:

•	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 amps being accepted.

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

•	Divide the reserve capacity by the number of amps 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 an ampere-hour charge equal to twice the reserve capacity rating, replace the battery. Refer to Battery Replacement or Battery Replacement in Engine Electrical.
8. After charging, load test the battery. Refer to Battery Load Test in Engine Electrical.