Activity: Battery Test Diagnosis Scenarios

Overview

Objectives

Students will:

1. Select the correct test method for a given situation
2. Calculate load test values from CCA ratings
3. Interpret test results and recommend actions
4. Identify when surface charge may affect results

Part 1: Load Test Calculations (10 points)

Instructions: Calculate the correct load test amperage for each battery.

Answer Key:

1. 250 amps
2. 325 amps
3. 400 amps
4. 362.5 amps (round to 363)
5. 500 amps

Part 2: Test Method Selection (10 points)

Instructions: For each situation, select the most appropriate test method and explain why.

Test Methods: A) Open-circuit voltage | B) Carbon pile load test | C) Conductance test

1. A customer brings in a car that was sitting in airport parking for 3 weeks. They want to know if the battery is still charged. (2 points)

Expected Answer: A — Open-circuit voltage. This is a quick charge check. The battery has been sitting long enough that surface charge is not a concern.

2. A customer complains that the engine cranks slowly every morning. The battery is a 2-year-old AGM rated at 750 CCA. (2 points)

Expected Answer: B or C — Load test or conductance test. The slow crank suggests the battery may have lost capacity. Either test will evaluate the battery's ability to deliver current. Load test is the industry standard; conductance is faster.

3. A tire shop wants to add a battery health check to every oil change service. They perform 30+ oil changes per day. (2 points)

Expected Answer: C — Conductance test. Fast (seconds per test), non-invasive, repeatable, and doesn't require full charge verification. Practical for high-volume screening.

4. A customer wants to file a warranty claim on a battery that is 2 years into a 3-year warranty. The dealer requires documented test results. (2 points)

Expected Answer: B — Carbon pile load test. Load testing is the industry standard for warranty claims and provides documented pass/fail evidence.

5. A technician just installed a new battery and wants to verify it's good before returning the car to the customer. (2 points)

Expected Answer: A + C — Open-circuit voltage to verify full charge, then conductance test to confirm the new battery meets its rated CCA. Quick and non-invasive verification.

Part 3: Diagnosis Scenarios (30 points)

Instructions: Read each scenario carefully. Determine the test result (pass or fail), identify the problem, and recommend the correct action.

Scenario 1 (6 points)

A 2019 Toyota Camry comes in for a no-start complaint. The battery is a flooded type rated at 600 CCA. The technician measures 12.6V OCV after the car sat overnight.

The technician performs a load test at 300 amps for 15 seconds. At the end of the test, the voltage reads 10.1V. Shop temperature is 72°F.

a) Is the test load correct? Why or why not? (2 points)

Expected Answer: Yes. 50% of 600 CCA = 300 amps.

b) Does the battery pass or fail? (2 points)

Expected Answer: Pass. 10.1V is above the 9.6V minimum at 70°F.

c) If the battery passes, what else should the technician check for the no-start? (2 points)

Expected Answer: Check the starter motor, starter circuit (cables, solenoid, relay), ignition switch, neutral safety switch, or anti-theft system. The battery has adequate capacity, so the no-start is caused by something else.

Scenario 2 (6 points)

A battery reads 12.7V immediately after the customer drives into the shop. The technician performs a load test and the battery passes at 9.8V.

Two hours later, another technician retests the same battery. OCV now reads 12.1V.

a) What happened between the two tests? (2 points)

Expected Answer: The first test was affected by surface charge. The 12.7V reading was temporarily inflated from the alternator charging during driving. After sitting for 2 hours, the surface charge partially dissipated, revealing the true OCV of 12.1V (approximately 50% charged).

b) Was the first load test result reliable? Why or why not? (2 points)

Expected Answer: No. Surface charge inflated the starting voltage, making it easier for the battery to stay above 9.6V during the load test. The battery should be fully charged and retested.

c) What should the technician do now? (2 points)

Expected Answer: Charge the battery fully (to 12.6V+ OCV with surface charge removed), then perform a new load test. The 12.1V reading indicates the battery is only about 50% charged.

Scenario 3 (6 points)

A conductance tester is used on a 3-year-old AGM battery rated at 800 CCA. The tester displays:

• Result: GOOD
• Measured CCA: 520
• Rated CCA: 800

a) The tester says "GOOD" — is the battery in like-new condition? (2 points)

Expected Answer: No. The battery passes the minimum threshold for "good" but has lost 35% of its original capacity (520 vs 800 CCA). It still functions but is significantly degraded.

b) Should the battery be replaced? (2 points)

Expected Answer: Not required right now since it passes, but the customer should be advised that the battery has lost significant capacity and may not perform well in cold weather. It should be monitored and will likely need replacement soon.

c) If this customer lives in a cold climate, would your recommendation change? (2 points)

Expected Answer: Yes. In cold climates, the reduced CCA (520 vs 800) may not be enough to start the engine reliably on the coldest days. Recommending proactive replacement before winter would be appropriate.

Scenario 4 (6 points)

A technician measures OCV on a flooded battery: 11.8V. Without charging first, the technician performs a load test at 50% of CCA. The voltage drops to 8.2V at 70°F.

a) What mistake did the technician make? (2 points)

Expected Answer: The technician performed a load test on a battery that was below 75% charge. At 11.8V, the battery is essentially dead (below 11.9V = 0% charge). The battery must be charged to at least 12.4V before load testing.

b) Is the 8.2V result valid? (2 points)

Expected Answer: No. The result is invalid because the battery was not adequately charged before testing. A discharged battery will always fail a load test regardless of its actual health.

c) What is the correct procedure? (2 points)

Expected Answer: Charge the battery fully (to 12.6V+ OCV), remove surface charge, verify at least 12.4V, then perform the load test. If the battery won't accept a charge or won't reach 12.4V, it may be sulfated or have a dead cell.

Scenario 5 (6 points)

A 2022 Ford F-150 has a battery rated at 850 CCA. The technician performs a load test on a January morning. Shop temperature is 25°F (-4°C). The voltage at the end of the 15-second load reads 9.0V.

a) What is the correct test load? (2 points)

Expected Answer: 425 amps (50% of 850 CCA).

b) Does the battery pass or fail at 25°F? (2 points)

Expected Answer: Pass. At 25°F, the minimum acceptable voltage is approximately 9.0V (interpolating between 30°F/9.1V and 20°F/8.9V). 9.0V meets the minimum threshold.

c) Would this same result (9.0V) be a pass or fail at 70°F? (2 points)

Expected Answer: Fail. At 70°F, the minimum is 9.6V. A reading of 9.0V would fail. Temperature correction matters — the same voltage can be a pass or fail depending on ambient temperature.

Submission

Students submit the completed worksheet with all calculations, selections, and scenario analyses.

Rubric