To solve the problems that a user cannot accurately predict a usable time of a portable telephone set because battery residual quantity display does not take the deterioration of a battery and temperature change into consideration and that the battery is consumed uselessly because data are written to a nonvolatile memory every time the user newly registers data.
A control part 4 updates data showing the residual capacity of the battery for terminal voltage of the battery 6 at any time to accurately calculate the usable capacity of the battery 6 regardless of the deterioration of the battery 6. Furthermore, the usable time is calculated with high accuracy and displayed by taking into consideration a radio wave state and temperature detected by a temperature detecting part 7. The control part 4 collectively backs up user data to a nonvolatile internal memory (flash memory) 4a to reduce power consumption used for backup, thereby extending the usable time.
MIKAMI TSUTOMU
Hiroshi Koyama
Hiroshi Takeuchi
Takahisa Shimada
Yuji Takeuchi
Katsumi Imae
Teshima Masaru
Atsushi Fujita
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