A charge state detecting device has a battery device including a plurality of batteries connected in series, a current sensor which detects a current flowing from the battery device, and a voltage sensor which detects the voltage of each of the batteries. A main controller calculates a correlation...http://www.google.de/patents/US5739671?utm_source=gb-gplus-sharePatent US5739671 - Device for accurate detection of remaining discharge capacities of a plurality of batteries 
