COMPOSITE BATTERY, AND COMPOSITE BATTERY SYSTEM PROVIDED WITH SAME

Provided are a composite battery that can maintain different operating temperatures of secondary batteries and accommodate variations in operating voltage caused by variations in environmental temperature, which are produced in an all-solid-state secondary battery, and a composite battery system including the composite battery. A composite battery 10 includes an all-solid-state secondary battery 12, a lithium ion secondary battery 14, an operating voltage holding device 16, and a housing 18. The all-solid-state secondary battery 12 operates under a predetermined temperature condition. The lithium ion secondary battery 14 is of a high-power type connected in parallel to the all-solid-state secondary battery 12. The operating voltage holding device 16 is for holding the operating voltage of the all-solid-state secondary battery 12 within a predetermined range. The housing 18 is formed of a heat-insulating member such that the inside of the housing 18 is thermally isolated from the outside of the housing 18. The all-solid-state secondary battery 12 is disposed inside the housing 18, and the lithium ion secondary battery 14 and the operating voltage holding device 16 are disposed outside the housing 18.