JP2776834B

If in the case of a load (R1) powered by a battery (6) the detection means (10) detect a battery voltage below a first threshold value (V1) defined by an adjustable voltage source (20), first time-measurement means (40, 50) measure the time interval during which the load (R1) is powered by the battery (6), at a voltage below this threshold value (V1). If subsequently the load (R1) is switched off and not connected to the mains voltage via a power-supply circuit (1), the battery (6) is discharged by a discharger (30). Second time-measurement means (40, 60) measure the time interval during which the discharger (30) is operative until the detection means (10) detect a battery voltage below a second threshold value (V2), which is defined by a voltage source (25) and at which the battery (6) may be regarded as fully discharged drained. After comparison of the sum of the time intervals measured by the first and the second time-measurement means with the reference value, correction means (70) correct the first threshold value (V1) in such a way that during a next discharge the time measured is better in agreement with the reference value.