Title: Module 3: OCV Test - Activity
Course: ASE A6 Battery Service > Section: Module 3: Battery Testing

Q: What does open-circuit voltage (OCV) tell you about a battery?
- Whether the battery can deliver its rated cranking amps
- How much charge the battery currently holds
- Whether the plates are sulfated
- The battery's internal resistance
A: How much charge the battery currently holds

Q: A fully charged 12-volt lead-acid battery should read approximately:
- 12.0V
- 12.2V
- 12.6V or higher
- 13.2V
A: 12.6V or higher

Q: A customer drives into the shop and you immediately measure 12.72V on the battery. This reading is most likely caused by:
- An overcharged battery that needs to be tested for overcharging
- Surface charge from the alternator — the reading is temporarily inflated
- A short circuit between the plates creating higher voltage
- A faulty multimeter giving an incorrect reading
A: Surface charge from the alternator — the reading is temporarily inflated

Q: What is the correct procedure to remove surface charge before taking an OCV reading?
- Disconnect the battery and wait 30 seconds
- Turn on the headlights for 2–3 minutes, turn them off, then wait 2 minutes
- Rev the engine to 3000 RPM for 1 minute
- Pour cold water on the battery case to cool it down
A: Turn on the headlights for 2–3 minutes, turn them off, then wait 2 minutes

Q: A battery reads 12.0V OCV after surface charge has been removed. What does this indicate and what should you do?
- 100% charged — proceed with load testing
- 75% charged — acceptable for further testing
- 25% charged — charge the battery before any further testing
- The battery is defective and should be replaced immediately
A: 25% charged — charge the battery before any further testing

Q: Using a real battery at your workstation, perform an open-circuit voltage (OCV) test. Before you begin, identify the battery you are testing — list the brand, CCA rating, and battery type (flooded or AGM) from the label. For the following questions (7–11), describe what you did during the test.
Feedback: The student should identify the battery brand (e.g., Interstate, DieHard, EverStart), the CCA rating from the label (e.g., 600 CCA), and the battery type (flooded or AGM).

Q: How did you prepare the battery for testing? Describe how you removed surface charge.
Feedback: Turned off all electrical loads. Applied a brief load by turning on the headlights for 2–3 minutes, turned them off, then waited 2 minutes for the surface charge to dissipate. Alternatively, the battery sat undisturbed for 12 hours.

Q: Where did you place your meter leads?
Feedback: Red lead on the positive (+) battery post, black lead on the negative (−) battery post.

Q: What voltage did you read on the multimeter?
Feedback: The student should report an actual voltage reading from their test (e.g., 12.6V, 12.4V, 12.2V, etc.).

Q: Using the state-of-charge table, what does your voltage reading mean? What percentage of charge does it represent?
Feedback: The student should correctly interpret their reading using the OCV table: 12.6V+ = 100% charged, 12.4V = 75%, 12.2V = 50%, 12.0V = 25%, 11.9V or below = discharged.

Q: Based on your OCV reading, what would you do next? Is the battery ready for further testing (conductance or load test), or does it need to be charged first?
Feedback: If the reading was 12.4V or higher, the battery is at least 75% charged and is ready for conductance or load testing. If the reading was below 12.4V, the battery must be charged before any further testing because a discharged battery will fail a load test even if it is healthy.