Estimate battery state of charge from resting voltage.
Voltage-based estimation only works at rest, because load or charging shifts terminal voltage substantially. Lithium chemistries have a very flat curve, making voltage a poor state-of-charge indicator for them. Coulomb counting is far more accurate than voltage for lithium, which is why battery management systems track charge in and out rather than relying on voltage.
Battery State of Charge
SoC % = (measured − empty voltage) ÷ (full − empty voltage) × 100
SoC % = (measured − empty voltage) ÷ (full − empty voltage) × 100 Voltage-based estimation only works at rest, because load or charging shifts terminal voltage substantially. Lithium chemistries have a very flat curve, making voltage a poor state-of-charge indicator for them.
Coulomb counting is far more accurate than voltage for lithium, which is why battery management systems track charge in and out rather than relying on voltage.
This calculator takes 4 inputs: Measured resting voltage, Voltage at full charge, Voltage at the discharge limit, Battery capacity. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.