BATTERY SYSTEM

Disclosed herein is a battery system (100) which includes: first and second battery modules (BM) connected between first and second system terminals (101, 102) in parallel; and a controller (130) controlling the first and second battery modules (BM). The first battery module includes a first battery (110) and a first main switch (121) , and a first balancing switch (122) and a first balancing resistor (123), which are connected to the first main switch (121) in parallel. The second battery module includes a second battery and a second main switch, and a second balancing switch and a second balancing resistor, which are connected to the second main switch in parallel. The controller is configured to detect a first battery voltage and a second battery voltage, and when an absolute value of a difference between the first and second battery voltages is greater than a first reference value, to open the first and second main switches and to close the first and second balancing switches.