A method and apparatus for battery gauging in a portable terminal are provided. In the battery gauging method, it is determined in a low-power mode whether a listening interval occurs for detecting the presence of a received signal. The remaining battery capacity is detected if the listening interval occurs. An interrupt signal is transmitted to the second processor, operating in a low-power mode, if the remaining battery capacity is less than or equal to a threshold. Upon receipt of the interrupt signal, the second processor wakes up to interrupt the power of the portable terminal.