Battery system management through non-linear estimation of battery state of charge

One or more non-transitory computer-readable media storing computer-executable instructions that when executed by a controller, cause the controller to perform a method of managing operation of a battery system, the managing comprising:

• identifying, in battery data representing actual performance of a battery system over a time period, sub-periods of charging or discharging in the time period, wherein the battery data comprises, for a plurality of times within the time period:
• operating mode, state-of-charge, output power or input power, and operating temperature;
• for the respective sub-periods of time, fitting a curve to the battery data corresponding to the time sub-period, the curve representing a change in state-of-charge of the battery system with respect to time versus state-of-charge of the battery system, time as a function of state-of-charge of the battery system, or state-of-charge of the battery system as a function of time;
• generating a performance model for the battery system using the curves for the respective sub-periods of time as well as output power and operating temperature corresponding to the curves, the performance model representing an expected performance of the battery system at different states of charge, operating temperatures, and output or input powers;
• and
• based on an expected use of the battery system, generating operating instructions for the battery system using the performance model.