PURPOSE: To display the residual use period of a battery in a time value according to the amount of energy consumed by adjusting a count speed according to the battery usage of an equipment, and operating a count circuit through the said count speed so as to carry out display.

CONSTITUTION: A signal corresponding to the state of a battery 2 is applied to a wave mode selector 4 from an equipment 1, which is connected to the battery 2, and is sent out into a count regulator 5 together with the temperature information of a temperature detector 10. Next, the signal sent into the regulator 5, after being regulated according to the frequency rate of the signal sent from an oscillator 9, is applied to a counter 6, and is divided by a given frequency rate. After that, the signal is converted into a time value by means of a decoder 7 which can be attached and detached, and the converted signal is displayed on a displayer 8. Consequently, since the residual capacity of the battery 2 can be accurately displayed in a time value, replacement and charging of the battery 2 can be carried out before the expiration of the battery capacity.