To provide a battery composed by compactly attaching thereto a current detector for detecting a supply current of the battery so as not to be influenced by an electrolyte.

A magnetic flux detection element H1 for detecting the size of magnetic flux in a core by forming a space in a part of the core made of a magnetic material and formed into a ring-like form is installed, and the current detector 35 for detecting the value of a current to be detected which flows through a current path penetrating the inside of the ring by an output signal of the magnetic flux detection element is formed by using a thermoplastic multilayered board. The formed current detector is formed by embedding it in an upper lid 36 of the battery so as to make an electrode column 31 for extracting a current from the battery 50 pierce the inside of the ring of the core.

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