Tools Required
Commercially available Battery Tester
Caution: Refer to Safety Glasses Caution in the Preface section.
Caution: Refer to Batteries Produce Explosive Gases Caution in the Preface section.
| • | For best results, use an automatic taper-rate battery charger with a voltage capability of 16 volts. |
| • | The charging area should be well ventilated. |
| • | Do not charge a battery that appears to be frozen. Allow the battery to warm to room temperature and test it using the battery charger. |
Battery State of Charge
Important: Using voltage to determine the batteries state of charge (SOC) is only accurate after the battery has been at rest for 24 hours. This is enough time for the acid in each cell to equalise. If the battery has been charged or discharged in the past 24 hours, the battery SOC will only be an estimate.
For maintenance-free batteries, SOC is estimated by reading the voltage of the battery across the battery terminals. Because the voltage is affected by current flow into or out of the battery, when checking the voltage the engine must be stopped and all electrical loads turned OFF, including parasitic loads. The voltage can also be affected if the battery has just been charged or discharged, so it is important to consider what has happened to the battery in the time just before testing. Use the following procedure to determine the batteries SOC:
- Be sure all electrical loads are turned OFF.
- Determine whether the battery has been used in a vehicle or charged within the past 12 hours.
- Estimate the battery temperature by determining the average temperature to which the battery has been exposed for the past 12 hours.
- Measure the battery voltage at the battery posts. Refer to the following table to determine the SOC according to the estimated battery temperature.
| • | If the answer is no, the terminal voltage will be stabilized and no action is necessary before reading the voltage. |
| • | If the answer is yes, terminal voltage will not be stabilized, wait 12 hours since the last time the battery was used/charged before continuing. |
Important: The state of charge table is accurate to 10 percent only after the battery has been at rest for 12 hours.
Use the SOC information as follows:
| • | A battery with a SOC that is below 65 percent must always be recharged before returning it to service or continuing storage. |
| • | A battery with a SOC that is 65 percent or greater is generally considered to be charged enough in order to be returned to normal service or in order to continue storage. However, if the battery is being used in slow traffic or with short drive times or if the temperature is very hot or very cold, the battery should be charged. to at least 90 percent, before returning it to service or continuing storage. |
Battery Voltage | % Charge at 0°C (32°F) | % Charge at 25°C (75°F) |
|---|---|---|
12.75 V | 100% | 100% |
12.7 V | 100% | 90% |
12.6 V | 90% | 75% |
12.45 V | 75% | 65% |
12.2 V | 65% | 45% |
12.0 V | 40% | 20% |
Charging Time Required
The time required to charge a battery will vary depending upon the following factors:
| • | Battery charger capacity-The higher the charger amperage, the less time it will take to charge the battery. |
| • | Battery SOC, a completely discharged battery requires more than twice as much charging time as a half charged battery. In a discharged battery with a voltage below 11 volts, the battery has a very high internal resistance and may only accept a very low current at first. Later, as the charging current causes the acid content to increase in the electrolyte, the charging current will increase. Extremely discharged batteries may not activate the reversed voltage protection in some chargers. Refer to the manufacturer's instructions for operating this circuitry. |
| • | Battery temperature, the colder the battery is the more time it takes to recharge the battery. The charging current accepted by a cold battery is very low at first. As the battery temperature increase the charging current will increase. |
Charging Procedure
Caution: Refer to Batteries Produce Explosive Gases Caution in the Preface section.
Flat batteries can be boost charged, avoid high charging current if the battery is more than 50 percent charged. Slow charging is required to fully charge the battery.
- Remove the battery from the vehicle.
- Inspect the battery for any physical damage, do not charge if battery is damaged.
- Loosen the battery filler caps, leave the caps resting on top of the filler tubes.
- Connect the battery charger, set to the appropriate charge rate.
- Monitor the electrolyte temperature, if it exceeds 55 percent turn off the battery charger and allow the battery to cool. After the battery has cooled restart charging at a reduced rate.
- For slow charging monitor the battery voltage, specific gravity and temperature every hour. Stop the charging when no change in voltage or specific gravity after three consecutive tests.
- Install the battery filler caps.
- After charging, test the battery.
- Install the battery to the vehicle.
Electrical Information
