A rechargeable battery system capable of suppressing the increase in the internal resistance of a lithium ion rechargeable battery and having long life is provided. A rechargeable battery system comprising rechargeable battery modules each having a plurality of lithium ion rechargeable batteries, and a charge/discharge control means for controlling assembled batteries having the rechargeable battery modules connected in parallel, in which the charge/discharge control means controls discharge, upon discharge of the lithium ion rechargeable batteries, on every lithium ion rechargeable battery modules connected in parallel is adopted.