There is provided a power storage system comprising a plurality of battery lines and a connection terminal unit. Each battery line comprises a plurality of battery cells arranged in a first direction. The connection terminal unit is electrically connected to terminal faces of each battery cell of a group of the battery cells, and the group of the battery cells is disposed in a second direction. At least one cut out is formed in the connection terminal unit. There are also provided a power storage system for a house, a power storage system for a vehicle, an electronic device and an electric vehicle including the power storage device. There is also provided a connection terminal unit for electrically connecting a plurality of battery cells, in which at least one cut out is formed in the connection terminal unit.