A battery is provided with an end-of-cell voltage indicating device which can be used to indicate the state-of-charge of the battery. The indicating device has a flexible substrate of the same peripheral configuration as the battery. The substrate has an indicating coating on one surface which is in...http://www.google.se/patents/US5525439?utm_source=gb-gplus-sharePatent US5525439 - Battery voltage tester for end of cell having indicator disposed on battery side
