An electrical system with replaceable batteries comprises an electrical system and a combined switch. The electrical system comprises a plurality of battery packs (1, 2, 3); all the battery packs are independently arranged each other; and an electric-quantity display device which is used for displaying the electric-quantity information indicating signals of the battery packs and a gear switch which is used for mutually switching the battery packs are arranged on the combined switch. Each battery pack comprises a battery (A1, A2, A3), a power switches (B1, B2, B3) and a battery management system (C1, C2, C3). The battery management systems receive and combine the output signals of the combined switches with the electric-quantity information indicating signals, thereby controlling whether the power switches are closed to provide power output or not.