Which statement about battery voltage testing is correct?

• A. Connecting the red DVOM lead to the negative battery post and the black DVOM lead to the positive battery post
• B. The voltage readings will be higher when the engine is running and lower when the engine is off
• C. Both statements are true
• D. Neither statement is true

Answer: (B)

When you test a 12-volt automotive battery, you’re looking at two states: engine off and engine running. With the engine off, the battery’s resting voltage is about 12.6 volts for a healthy full-charge battery. When the engine is running, the alternator charges the system and raises the voltage to roughly 13.8–14.4 volts. So the reading tends to be higher during operation than when the engine is off, which is the behavior described and why that statement is correct.

Regarding how to measure, the proper procedure is to place the red voltmeter lead on the positive battery terminal and the black lead on the negative terminal. Reversing the leads would give an incorrect reading. That explains why the statement about the leads in the other option isn’t correct, reinforcing why the higher-with-engine-running description is the best answer.