Battery – State of Charge Test
The first step when conducting starting and charging system
tests is to verify that the battery is fully charged.
1. Place the vehicle ignition switch in the OFF position.
2. Turn the Hi-Beams ON for 30 seconds to dissipate the battery surface charge.
3. Turn the vehicle lights and accessories OFF.
4. Set DMM to DC Volts (range closest to 12 volts).
5. Connect black test lead to battery negative post.
6. Connect red test lead to battery positive post.
· 12.6V or above Fully Charged
· 12.4 – 12.5 V 50-75% Charged
· Under 12.3V Needs charging
Battery - Parasitic Load Test
Several devices on a modern vehicle are continuously using small amounts of current to function and retain their memory. Usually, about 30mA is all that is necessary to maintain the computer memory after all the various accessories and modules are inactive. This can vary - check the service manual for the vehicle in question.
1. Place the ignition switch and all vehicle accessories in the OFF position.
2. To avoid blowing a fuse in the meter - verify that total current draw is under the maximum current reading ability of your meter. Use an ACM6100 clamp-on adapter or equivalent.
3. Disconnect the vehicle negative (-) cable.
4. Turn the meter ON.
5. Select DC Amps.
6. Plug the black test lead into the COM input.
7. Plug the red test lead into the “A” input.
8. Connect the black COM probe tip to the battery negative post.
9. Connect the red “A” lead probe tip to the battery negative cable - this will complete a circuit allowing the measurement of parasitic load.
After verifying that parasitic load is under 2 amps, where possible, select a more sensitive scale such as “mA” or “μA” and move the red lead to the appropriate meter input. This will change the readout from amps to milliamps and give the most accurate reading for small current flow.
Battery - Cranking Voltage Test
1. This is a Cranking Test - Disable ignition or fuel so that the engine will not run.
2. Set DMM to DC Volts (range closest to 12 volts).
3. Connect black test lead to battery negative post.
4. Connect red test lead to battery positive post.
5. Crank engine for 15 seconds.
6. Note voltage reading from the DMM during the last three seconds of cranking:
· 9.6 V (or higher) means battery is OK
· 9.5 V (or lower) usually indicates one of
the following conditions:
- Excessive connector/cable resistance
- Faulty battery