Abstract: The present invention relates to a battery pack for supplying power to a portable radiotelegraphic unit. The battery pack comprises a rechargeable battery whose voltage varies with time in such a manner that is residual capacity can be estimated from the detected voltage of the battery, a voltage detector for detecting the voltage of the battery, and an indicator for visibly displaying the voltage detected by the voltage detector. With the above construction, the battery can be recharged when the battery voltage reaches a lower value and the discharging of the battery can be stopped when the battery voltage reaches an upper value. As a result, the battery is prevented from the overcharging and overdischarging, and the life and reliability of the battery are increased.