In standardized examination-rooms, candidates are prohibited from using personal timekeeping devices, while wall-mounted BPC time-code radio-controlled clocks (RCCs) in complex buildings often suffer from reception blind spots, unstable synchronization, and frequent battery replacement. To address this, a unified time-keeping scheme combining a “life-time powered mechanical RCC” with a “local BPC miniature transmitter” is proposed. On the terminal side, the WBC-E16A exam clock retains its original appearance, but its two AA cells are upgraded to a 2S4P low-self-discharge AA pack, and an mWh-level energy model is derived from constant-resistance discharge tests and in-situ power measurements. On the infrastructure side, a≤1.5 W USB 5 V transmitter is developed that acquires UTC from multiple NTP servers over campus WiFi and rebroadcasts the standard BPC code inside classrooms. Tests with ten clocks in a fully enclosed underground space show that, in BPC reception blind spots, all terminals automatically complete their first synchronization within 2~10 minutes. In a four-week field trial with thirty clocks in a teaching building, the automatic synchronization success rate increases from about 70% to 100% after enabling the local transmitter. Discharge and consumption measurements indicate that Nanfu IoT AA cells provide about 34.9 Wh of usable energy above 2.2 V; combined with a daily consumption of 14.8~16.5 mWh and a 1%~2% self-discharge rate, a single 2S4P pack can support at least five years of operation without battery replacement. The scheme has been deployed in about 7 848 terminals across 22 provincial-level regions, and the proposed Life-Time RCC plus local BPC blind-spot compensation enables long-term, second-level synchronization of mechanical wall clocks while greatly reducing maintenance and inspection workload and significantly enhancing the robustness of examination-room timekeeping.