U.S. Philips Corporation

Jean N Patillon

Johann R Van Beek

Robert E Einerhand

A battery-powered electrical device comprising a switchable voltage drain (3,5) and a rechargeable battery (1), and further comprising means for measuring the voltage V across the terminals of the battery (1) as a function of cumulative discharge time t, and for determining the cumulative discharge time t.sub.p corresponding to the attainment of the local extremum of least magnitude in the derivative dV/dt. In a particular embodiment, the device contains means for interrupting the voltage drain (3,5) upon expiry of a cumulative discharge time t.sub.e =nt.sub.p, whereby n is a fixed, pre-selected real number. In addition, it is possible to calculate and display the remaining discharge time t.sub.rem =m.sub.o t.sub.o -t, where m.sub.o is a fixed, pre-selected real number. The values of n and m.sub.o will generally be chosen to lie in the range 1.2-6.

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Paris, France

Jean N Patillon