A hybrid model to determine state-of-charge for lithium batteries includes both a physical model and an empirical or data-driven model. The physical model is an electrochemical model, based on the battery materials properties and structure and describes dynamic electrochemical reactions. The empirical model uses coulomb counting and a relaxation filter, plus a Kalman filter for adaptive compensation of the system parameters. In some SOC regimes, one model is strongly favored over the other. In some SOC regions, a weighted combination of the two models is used.
STATEMENT OF GOVERNMENT SUPPORT
 The invention described and claimed herein was made in part utilizing funds supplied by the U.S. Department of Energy under Contract No. DE-0E0000223. The Government has certain rights in this invention.