State-of-charge indication in portable applications

The known methods of state-of-charge (SoC) indication in portable applications are not accurate enough under all practical conditions. The method presented in this paper aims at designing and testing an SoC indication system capable of predicting the remaining capacity of the battery and the remaining run-time with an accuracy of 1 minute or better under all realistic user conditions, including a wide variety of load currents and a wide temperature range. The basis of the proposed algorithm is current measurement and integration during charge and discharge state and voltage measurement during equilibrium state. One of the main problems in designing an accurate SoC indication system is aging of the battery. A simple method of adapting the maximum battery capacity used in the system with the aging effects is presented in this paper. A first set of experimental results shows the effectiveness of our novel approach for improving the accuracy of the SoC indication.