1497222 Indicating the discharge of batteries P R MALLORY & CO Inc 18 March 1975 [5 April 1974] 1115675 Headng H1B In order to indicate the discharge of a battery comprising series connected cells, which may be used in, e.g. an alarm system, the cells have the same operating life, discharge capacity and first electrode (Zn), but at least one of the cells has a second electrode different from the second electrode of at least some of the cells. The voltage of the battery is continuously monitored, and the cells having the different second electrodes are such as to produce an abrupt voltage drop, after a predetermined time, and thus allow the battery to be replaced before it is wholly exhausted. The second electrode may be (wt.%) 89 HgO, 6 MnO 2 and 5 graphite, and the "different" second electrode may be 45 HgO, 3 MnO 2 , 45 CdO, and 7 graphite.
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