Battery system

A battery system comprising:

• a pair of output terminals connected to a load;
• battery modules connected to the pair of output terminals and disposed in parallel to each other;
• and
• a controller, wherein
• each of the battery modules includes
• a battery unit including cells connected in series to each other,
• a main relay provided on a first side end portion of the battery unit,
• a unit relay provided on a second side end portion of the battery unit, and
• a pre-charging unit provided in parallel to the main relay,
• the pre-charging unit of each of the battery modules includes
• a pre-resistor, and
• a pre-charging relay connected in series to the pre-resistor,
• the controller includes a pre-charging process executor configured or programmed to, when the battery modules are to be connected to the load through the pair of output terminals, exercise control so as to connect the battery modules to the pair of output terminals after having executed a pre-charging process on the battery modules on a one-by-one basis, and
• the pre-charging process involves switching OFF the main relay of a targeted one of the battery modules and switching ON the unit relay and the pre-charging relay of the targeted one of the battery modules, and the pre-charging process then involves switching ON the main relay of the targeted one of the battery modules and switching OFF the pre-charging relay of the targeted one of the battery modules when a difference between a main voltage carried between the pair of output terminals and a unit voltage across the battery unit of the targeted one of the battery modules is equal to or smaller than a predetermined threshold value.