Technician A says that the battery voltage should be 12.0-12.2 VDC with the alternator not operating. Technician B says that the voltage should be 14.0-14.1 VDC with the alternator operating. Who is right?

• A. A
• B. B
• C. Both A and B
• D. Neither A nor B

Answer: (D)

The voltage readings show the battery’s state of charge and whether the charging system is working. When the engine is off, a healthy, fully charged battery should read about 12.6 volts. A reading in the 12.0–12.2 volt range suggests a battery that’s quite discharged or not healthy, not a healthy static reading for a standby battery. So the first technician’s statement isn’t correct for a healthy battery with the engine not running.

When the engine is running, the alternator should push charging voltage into the system, typically around 13.8–14.4 volts. A reading in that general range is expected, though exact acceptable values can vary slightly by vehicle. The suggested 14.0–14.1 volts is generally within the normal charging range, but depending on the specific vehicle spec and tolerances, it may not match the exact specification used in the reference material. In other words, the ranges given don’t align with the standard values used for both conditions, so neither statement matches the typical expected values.

To check properly, measure with the engine off and ignition off for the standby battery voltage (around 12.6 V for a healthy battery), and measure with the engine running at a moderate idle to confirm charging volts (roughly 13.8–14.4 V).