State of Energy (SoE)
State of energy (SoE) is an estimate of the battery energy that remains available, expressed relative to a defined energy baseline.
How it differs from state of charge
State of Charge (SoC) tracks remaining electric charge, commonly in ampere-hours or as a percentage of charge capacity. SoE tracks energy, normally in watt-hours or as a percentage of a stated available or nominal energy value. Because battery voltage changes across the operating window and under different conditions, the same charge fraction does not necessarily represent the same energy fraction.
A BMS estimates SoE from battery measurements, accumulated power flow, and a model of battery behaviour. The result depends on the chosen baseline, operating limits, temperature, and assumptions about usable energy; it should not be read as a direct energy measurement unless the method says so.
For the underlying state-estimation methods, see Battery Management System. For the difference between rated and driver-accessible energy, see Gross and Net Battery Capacity.