A battery terminal is configured to be secured to a battery case and includes a terminal assembly, and a ring. The light transmission function member is any one of a transparent portion, translucent portion, light diffusion portion, or opening portion, and the light source 2L is arranged on its lower side. The body includes a) a threaded portion and an unthreaded portion and b) an aperture extending radially from the unthreaded portion. Source-drain regions are formed in the first semiconductor layer.