The present invention provides a secondary power supply for the telematics terminal. A secondary power supply for a telematics terminal including. a power control unit for controlling a power supply based on a power control signal of the telematics terminal and/or a start-up key signal; a telematics control unit which is operated by power supplied from a secondary power supply unit under the control of the power control unit and controls each of components inside the telematics terminal; the secondary power supply unit for supplying the power to the telematics control unit; and a rectifying unit for rectifying power from a main power supply unit one more time and protecting the components from a reverse voltage by opening the connection of the main power supply unit and the secondary power supply unit when a voltage level of the secondary power supply unit is higher than that of the main power supply unit.