A battery system includes a battery and a battery protection apparatus. The battery protection apparatus protects the battery from over-discharge. The battery protection apparatus includes a voltage controlled switch, a start switch, and a voltage detecting unit. The voltage controlled switch establishes an electrical connection between the battery and the load. The start switch turns on the voltage controlled switch when actuated. The voltage detecting unit detects a battery voltage of the battery and generates a detecting voltage according to the battery voltage. The voltage controlled switch is turned off when the detecting voltage is lower than a predetermined value.