A total power failure is defined as which combination?

• A. No AC input power with battery voltage below 9.5 VDC
• B. Battery voltage below 7 VDC with AC input present
• C. Battery voltage below 9.5 VDC with no AC input
• D. Battery voltage above 9.5 VDC with AC input present

Answer: (C)

Total power failure happens only when the system loses its external power source and the internal battery is too depleted to carry the load. The defining condition uses two parts together: there is no AC input power, and the battery voltage has fallen below 9.5 V DC. If the AC supply is still present, the system can run from the outlet even if the battery is low, so it isn’t considered a total power failure. If there’s no AC input but the battery voltage is still above 9.5 V DC, the system can continue on battery power for a while, so it’s not yet categorized as total power failure. The 9.5 V threshold marks a level below which the battery can no longer reliably support the required loads.