Question: what should car battery voltage be when off?
Answer: Car Battery Voltage When the engine is running, that number should be between 13.7 and 14.7 volts. If the battery is reading at 12.4 volts, then it's 75% charged. At 12 volts, it drops to 25%. Once the battery reads at 11.8 volts, it's considered to be completely discharged.