While an open circuit voltage test determines the battery's state of charge, it does not measure the battery's ability to deliver adequate cranking power. A capacity, or heavy-load, test does. A Sun VAT-40 tester is used. If another type of tester is used, follow the manufacturer's recommended procedure.
The following steps outline a typical procedure for load testing a battery:
1. Test the open circuit voltage. The battery must be at least half charged. If the open circuit voltage is less than 12.4v, charge the battery.
2. Disconnect the battery cables, ground cable first.
3. Prepare the tester:
• Rotate the Load Increase control to OFF.
• Check each meter's mechanical zero. Adjust, if necessary.
• Connect the tester Load Leads to the battery terminals; RED to positive, BLACK to negative.
• Set Volt Selector to INT 18V. Tester voltmeter should indicate battery open-circuit voltage.
NOTE: Battery open-circuit voltage should be at least 12.4 volts (75% charged). If not, the battery requires charging.
• Set Test Selector to #2 CHARGING.
• Adjust ammeter to read ZERO using the electrical Zero Adjust control.
4. Connect the clamp-on Amps Pickup around either tester load cable (disregard polarity).
5. Set the Test Selector Switch to #1 STARTING.
6. Load the battery by turning the Load Increase control until the ammeter reads 3 times the amp-hour (AH) rating or one-half the cold-cranking ampere (CCA) rating.
7. Maintain the load for no more than 15 seconds and note the voltmeter reading.
9. If the voltmeter reading was 10.0 volts or more, the battery is good. If the reading is 9.6 to 9.9 volts, the battery is serviceable, but requires further testing. Charge and re-test. If the reading was below 9.6 volts, the battery is either discharged or defective.
NOTE: Test results will vary with temperature. Low temperatures will reduce the reading. The battery should be at operating temperature.
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