Federal inspectors said Monday they will ratchet up scrutiny of the San Onofre nuclear power plant after discovering that a battery meant to power safety systems had been inoperative for four years. Plant personnel discovered in March that bolts connecting an emergency battery to a circuit breaker were loose, a problem the Nuclear Regulatory Commission attributed to poor maintenance. The commission said that the twin-reactor plant near San Clemente, run by Rosemead-based Southern California Edison, remains safe, and that other backup batteries are functioning. But the commission expressed concern that the battery problem had gone unnoticed from 2004 to 2008....