To provide a battery system that can detect connecting locations of a plurality of battery packs with a simple structure, the battery system includes a plurality of terminal blocks 21 to 24 to which the plurality of battery packs 11 to 14 are connected. Each battery pack includes a first battery power supply terminal 15, a second battery power supply terminal 18, and a battery ID terminal 17. A power supply voltage is applied between the first and second battery power supply terminals 15, 18, and the battery ID terminal 17 divides the power supply voltage into a first voltage to be applied between the first battery power supply terminal 15 and the battery ID terminal 17, and a second voltage to be applied between the second battery power supply terminal 18 and the battery ID terminal 17, when the battery pack is connected to the terminal block. A voltage dividing ratio of the first voltage or the second voltage with respect to the power supply voltage is made to be different among the plurality of battery packs depending on the terminal blocks, and the control circuit 2 detects the voltage dividing ratio and determines the terminal blocks to which the battery packs are connected.