State-of-charge indicators [batteries]

Summary form only given. Prediction of the capacity remaining in used batteries is important information to the user. Each year millions of dollars are spent on batteries for use in portable electronics equipment. In order to maintain readiness, users currently replace batteries on a conservative schedule. This practice results in the waste of millions of dollars in battery energy every year-approximately 40 percent of available battery capacity. For many battery systems there is no convenient method of determining the available capacity remaining in partially used batteries; hence, users do not take full advantage of all the available battery energy. Knowledge of capacity remaining in used batteries results in their better utilization. It is a well documented and accepted that the available capacity in a battery is a function of the conditions that the battery has been subjected. Capacity remaining is a complex function of current drain, temperature and time. A continuous internal means of determining remaining capacity is desirable. These internal methods require extensive calibration and in many cases are difficult to implement. The pursuit of a universal state-of-charge indicator has been elusive due to the variation in behavior of battery systems. Reliable methods of predicting remaining capacity has been actively sought. This presentation describes different methods of determining battery state-of-charge and the application of these methods to different battery systems