An average circuit voltage on a 12-volt system is

• A. 11.5 to 12.5 volts
• B. 13.8 to 14.8 volts
• C. 10.0 to 12.0 volts
• D. 12.6 to 13.0 volts

Answer: (B)

When the engine is running, the charging system (alternator) pushes the system voltage above the nominal 12 volts to charge the battery and supply electrical loads. The typical charging voltage for a 12-volt system is around 13.8 to 14.4 volts, and it can reach up to about 14.8 volts in some cases. So the range that matches normal charging is 13.8 to 14.8 volts. Resting battery voltage sits around 12.6 volts, and other ranges reflect undercharging or resting conditions rather than the charging state.