Battery load testing involves measuring the amperes produced by a charged battery and is particularly relevant for vehicle batteries. The battery in a car or truck needs to produce high amperes to power the starter motor and turn the vehicle's engine. The term used to describe the battery's power is "cold cranking amps" or CCA. To do an accurate battery load test, you need to use a battery load tester.
Charge your battery fully to get an accurate load test reading. Examine the label on the battery to ascertain the output voltage and then use a multimeter to check that the voltage reading is the same as that indicated on the battery label.
Set the multimeter to "Voltage." Connect the red sensor from the meter to the positive battery terminal and attach the black sensor to the negative terminal. The battery terminals are labelled "+" and "-" for convenient identification. Read the meter. If the reading is more than 10 per cent lower than the voltage on the battery label, you need to charge the battery before doing a load test.
Remove the sensors from the battery terminals.
Examine the battery label to determine its ampere rating. You will see "CCA" followed by a number that denotes the cold cranking amps. Divide this number by two on your calculator to arrive at the optimum figure for your load test. For example, if the battery label reads CCA 500, then divide 500 by 2 to get 250. Jot down the result of your calculation.
Attach the load tester sensors to the battery terminals. Again, connect the red lead to the positive battery terminal and the black lead to the negative terminal as you did earlier.
Look at your watch or a timer. Leave the sensors connected to the battery posts for 15 seconds. Then, read the measurement on the load tester and compare it to the number that you calculated in Step 4. If the reading is more than 15 to 20 per cent below that number, it indicates your battery is not able to produce the correct power and won't be able to get your engine running. Remove the sensors from the battery posts and replace the battery if necessary.