To output a stable battery voltage drop signal never influenced by the dispersion in discharge characteristic curve of the battery by providing the subject device with, as essential constitution, a voltage drop quantity increase/decrease comparing part for judging the voltage drop quantity increasing tendency, and a voltage dropping ratio comparing part for judging that the voltage dropping ratio reaches a prescribed value.
The voltage of a battery is measured by a battery voltage measuring part 1. The battery voltage measured every lapse of a prescribed fixed time is subjected to a voltage drop quantity increase/decrease comparison of the differential voltage Vsa between the battery voltage Va-1 measured last time and the battery voltage Va measured this time with the differential voltage Vsn between the battery voltage Va-1 measured last time and the battery voltage V.=2 measured the time before last by a voltage drop quantity increase/decrease comparing part 2. The battery voltage dropping ratio Pc is compared with a battery voltage dropping ratio Ps set by a voltage dropping ratio setting part 4 by a voltage dropping ratio comparing part 5.
KAMIYAMA YASUSHI
SADA NORIBUMI
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