Battery Service

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OPEN CIRCUIT VOLTAGE
A digital voltmeter must be used to check the battery's open-circuit voltage. Analog meters are not accurate and cannot be used.

1 . Turn on the headlamps' high beam for several minutes to remove any surface charge.

2. Turn headlamps off, and connect the digital voltmeter across the battery terminals.

3. Read the voltmeter. A fully charged battery will have an open-circuit voltage of 12.6 volts. On the other hand, a totally dead battery will have an open-circuit voltage of less than 12.0 volts.

Note: If the battery is 12.4v or higher, proceed to heavy load test. If the battery is less than 12.4v, the battery must be fully recharged before testing. Be sure to remove the surface charge completely; this is the number one mistake technicians make. If need be, place a load tester on the battery and load the battery for 10 seconds at approximately 200 amps. Allow a few minutes for the battery to recover then measure the open circuit voltage. This should remove the surface charge and allow an accurate open circuit voltage measurement. (Remember: a reading of 12.4 volts or higher load test the battery, 12.3 volts or less, recharge the battery.)

% of charge 12.6v = 100% 12.4v = 75% 12.2v = 50% 12.0v = 25% 11.9v = 0%