To provide a water electrolysis hybrid storage battery capable of preventing overcharge without providing an expensive protective switch, or the like, corresponding to a high current and a large voltage and preventing burst, firing, and the like, of an enclosed storage battery such as a lithium ion storage battery due to overcharge of the emergency.

In a water electrolysis hybrid storage battery consisting of a virtual battery 32 constituted of parallel connection of enclosed storage batteries and water electrolytic device 26A, i.e., electrochemical cells using an aqueous solution as an electrolyte, or of a series connection of a plurality of virtual batteries, when overcharge energy leading to overcharge of the enclosed storage batteries is applied to the virtual battery, the water electrolytic device absorbs energy by performing electrolysis reaction of water, and prevents the charging voltage of the virtual battery from reaching the overvoltage dangerous voltage of the enclosed storage batteries.