Described is system and method for controlling power of a computing terminal with an external power source. In particular, a voltage is measured within a system using a voltage detector of a computing terminal. The system includes a battery which provides power to the system and the terminal. When the measured voltage changes to a first level, a first procedure is initiated to monitor the voltage for a time period. Upon expiration of the time period, if the monitored voltage has not changed to a second level, a second procedure is initiated to power off the terminal.