A method for determining the state-of-charge for zinc mercuric oxide type primary cells. I-V curves of the cells are plotted and the nearly constant slopes of these I-V curves above 75mA are measured graphically. These slopes are used to define effective differential DC resistance values (.DELTA.V/.DELTA.I).sub.75mA...http://www.google.co.uk/patents/US3997834?utm_source=gb-gplus-sharePatent US3997834 - State-of-charge indicator for zinc-mercuric oxide primary cells
