with the value of a current flowing therethrough and comprises a first resistor and a second resistor connected in series and a switch element connected in parallel to the second resistor when current is low the switch is operated so that current flows through the first and second resistors so that increased detection accuracy is possible when is high the switch is operated so that current flows only through the first resistor so that detection accuracy remains high but power dissipation is not increased application_number US 12990298 A description in the above mentioned charge and discharge control circuit and the chargeable power supply unit of the present invention sensing resistor value varies in accordance with charge and discharge current for large charge and discharge current a small sensing resistance is selected so as to reduce loss of charge and discharge current voltage value is sufficient to detect even voltage fall of the sensing resistor and the detecting accuracy is high because of the low amplification factor of the operational amplifier in contrast for small charge and discharge current voltage value is sufficient to detect even voltage fall of the sensing resistor because of the high resistance value of the sensing resistor and the detecting accuracy is high because of the low amplification factor of the operational amplifier.