An electric construction machine comprising: an electric motor; a hydraulic pump that is driven by the electric motor; a plurality of hydraulic actuators (13A, 13B, 19 to 21) that are driven by hydraulic fluid discharged from the hydraulic pump; and a battery device that serves as an electrical power source for the electric motor; wherein the battery device includes a plurality of battery systems (56A, 56B) that each have a plurality of batteries and are mutually parallel-connected, wherein the electric construction machine includes connection change control means (32, 54A, 54B, 58A, 58B; 32A, 54A, 54B, 58A, 58B) that can change the connections of the battery systems (56A, 56B) to select one of the battery systems (56A, 56B)and let the selected battery system supply electrical power to the electric motor, characterized by display means for indicating a battery system that supplies electrical power to the electric motor, and in that the batteries are series connected, and by further comprising: a plurality of remaining battery power amount acquisition means (54A, 54B) that acquires information about the amount of electrical power remaining in each of the battery systems; motor stop control means that stops the electric motor when a battery system supplying electrical power to the electric motor is exhausted; and inverter means that automatically selects a battery system other than the exhausted battery system when a preselected period of time elapses after the electric motor is stopped by the motor stop control means; wherein the connection change control means (32, 54A, 54B, 58A, 58B) changes the connections of the battery systems so that the battery system selected by the inverter means supplies electrical power to the electric motor. an electric motor; a hydraulic pump that is driven by the electric motor; a plurality of hydraulic actuators (13A, 13B, 19 to 21) that are driven by hydraulic fluid discharged from the hydraulic pump; and a battery device that serves as an electrical power source for the electric motor; wherein the battery device includes a plurality of battery systems (56A, 56B) that each have a plurality of batteries and are mutually parallel-connected, wherein the electric construction machine includes connection change control means (32, 54A, 54B, 58A, 58B; 32A, 54A, 54B, 58A, 58B) that can change the connections of the battery systems (56A, 56B) to select one of the battery systems (56A, 56B)and let the selected battery system supply electrical power to the electric motor, characterized by display means for indicating a battery system that supplies electrical power to the electric motor, and in that the batteries are series connected, and by further comprising: a plurality of remaining battery power amount acquisition means (54A, 54B) that acquires information about the amount of electrical power remaining in each of the battery systems; motor stop control means that stops the electric motor when a battery system supplying electrical power to the electric motor is exhausted; and inverter means that automatically selects a battery system other than the exhausted battery system when a preselected period of time elapses after the electric motor is stopped by the motor stop control means; a plurality of remaining battery power amount acquisition means (54A, 54B) that acquires information about the amount of electrical power remaining in each of the battery systems; motor stop control means that stops the electric motor when a battery system supplying electrical power to the electric motor is exhausted; and inverter means that automatically selects a battery system other than the exhausted battery system when a preselected period of time elapses after the electric motor is stopped by the motor stop control means; wherein the connection change control means (32, 54A, 54B, 58A, 58B) changes the connections of the battery systems so that the battery system selected by the inverter means supplies electrical power to the electric motor.