To provide a battery system in which harmful effect due to dew condensation water is prevented by promptly removing the dew condensation water, and which is safely used in various temperature and humidity environments.

The battery system includes: a battery block 2 formed by laminating a plurality of rechargeable square batteries 1 while their planes are opposed to each other; heaters 3 thermally bonded to the square batteries 1 of this battery block 2; and a cooling mechanism 20 for cooling the square batteries 1 of the battery block 2. Furthermore, in the battery system, water absorbing layers 5 are disposed on opposing laminated surfaces of the square batteries 1, these absorbing layers 5 absorb either or both of the dew condensation water and leaked electrolyte solution of the square batteries 1, and then the absorbed liquid is heated by the heaters 3 for removal.