A comparator (10) compares the voltage of a battery (2) with a switchable reference voltage (Uref1A, Uref1B, 18) and supplies a signal (IS) if the voltage of the battery passes the reference voltage. The switching point of the reference voltage is defined by means of a first resistor (32). By means of the first resistor the number of cells of the battery is set to one or two. A second resistor (6) in series with the battery enables an additional voltage to be obtained in order to correct the reference voltage for the type of battery cell used.
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