For 1990-2009 cars

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.

• | Some time may pass before the battery accepts current in excess of a few milliamperes.

2. Set the battery charger to 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 in order 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. This function will turn on the charger 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 may take up to 16 hours before the battery appears to be accepting current.
5. Perform the following calculation in order to determine the amount of time that the battery may need to be charged:

• | 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 Temperature Versus Voltage Drop .

• | Divide the reserve capacity by the number of amps shown on the meter in order 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 .
8. After charging, load test the battery. Refer to Battery Load Test .