Abstract: In a method for charging a secondary battery (21), for determining, by a detection of ??V which is observed when a battery voltage is decreased by ?V from a peak voltage, that the secondary battery (21) is fully charged, an invalid time for invalidating a detection of the peak voltage and the detection of ??V is set; the invalid time is calculated by dividing a current integrated quantity of a rapid charge current caused to flow in the secondary battery (21) by an average charge current quantity at a time of the rapid charge; and determining that the secondary battery (21) is fully charged, by the detection of ??V which is observed when the battery voltage of the secondary battery is decreased by ?V from the peak voltage after a lapse of the invalid time from a start of the charging of the secondary battery (21).

Abstract: A hair growth device includes a first light irradiator configured to irradiate an invisible light of invisible wavelength range, for hair growth; and a second light irradiator configured to irradiate a visible light of visible wavelength range. The second light irradiator is configured to direct the visible light to either inside of a light irradiation area of the light from the first light irradiator or outer circumference of the light irradiation area.