A battery power measuring system for a Battery-Backed SRAM includes a nonvolatile memory (11), a clock (12), a CPU (10) and a buzzer (13). The nonvolatile memory is for storing a system time, an estimated battery maximal endurance, an estimated battery minimal endurance, and a cumulative on-battery run time. The clock is for indicating the current system time. The CPU is for calculating a new cumulative on-battery run time and a remaining battery endurance. The buzzer is for reminding users to replace a battery when the remaining battery endurance is lower than the estimated battery minimal endurance. The CPU is connected to the nonvolatile memory, the clock, and the buzzer through a plurality of data buses (14). A related battery power measuring method is also provided.