To provide a fast charger and a fast charging method that are highly efficient in fast charging of a solid-state battery.
A fast charger includes a charging section, a temperature acquisition section, and a controller. The charging section feeds current to a solid-state battery being a secondary battery. The temperature acquisition section acquires a temperature of the solid-state battery. The controller performs control to cool the solid-state battery if the temperature acquired by the temperature acquisition section is greater than or equal to a predetermined temperature.
The controller determines a plurality of inflection points on a curve representing changes in the temperature of the solid-state battery against internal resistance of the solid-state battery. The predetermined temperature corresponds to an inflection point on a high-temperature side among the plurality of inflection points.