A battery charger in one aspect of the present disclosure includes an attachment portion, a charging circuit, a positive electrode terminal, a negative electrode terminal, at least one signal input terminal, an analog value acquisition device, a charging current detector, a comparison processor, and a current value reflection processor. The current value reflection processor performs one of a variable determination process for reference values and an analog value correction process. The variable determination process is a process for the current value reflection processor to variably determine the reference value based on a value of a charging current detected by the charging current detector. The analog value correction process is a process for the current value reflection processor to correct an analog value to be used in a comparison by the comparison processor based on the value of the charging current detected by the charging current detector.