In previous decades, automobile batteries were used to start the car. Now, with stop-start technologies and renewed interest in electric vehicles, automotive battery management systems must be more accurate and sophisticated. Most battery management systems use different correlates (typically, voltage measurements or Coulomb counting) to estimate how much energy remains within the battery. The efficacy of these estimation techniques is sub-optimal because they rely on correlative data sources. Described herein is a novel approach that precisely determines the state of charge for lead-acid and lithium ion batteries by directly measuring the material changes within the battery across different states of charge. Directly assessing the material state of the battery assures very accurate monitoring - at maximum, there is a 5% discrepancy between any single estimated data point and actual state of charge for lead-acid batteries and lithium iron phosphate batteries, with the average error being less than 2%.