Methods and apparatus for updating a fuel gauge and estimating state of health of an energy storage cell

A method of updating an active fuel gauge of a energy storage cell, the method comprising:

• receiving a first resting voltage measurement of the energy storage cell, the first resting voltage measurement measured at a first time,
• receiving a second resting voltage measurement of the energy storage cell, the second resting voltage measurement measured at a second time after the first time,
• receiving a third resting voltage measurement of the energy storage cell, the third resting voltage measurement measured at a third time after the second time,
• calculating a first difference in capacity between a first pair of the first, second, and third resting voltage measurements and a second difference in capacity between a different pair of the first, second, and third resting voltage measurements based on a first voltage and state of charge (SOC) relationship stored in a memory and corresponding to the active fuel gauge of the energy storage cell,
• determining whether the first and second differences are equal to each other and to a reference capacity difference, and
• when the first and second differences are equal to each other and to the reference capacity difference, identifying an estimate of a remaining capacity of the energy storage cell corresponding with the active fuel gauge, or
• when the first and second differences are not equal to each other or to the reference capacity difference:
• identifying a second voltage and SOC relationship having capacity differences between pairs of the first, second, and third resting voltage measurements that are equal to each other, and
• updating the active fuel gauge in the memory based on the identified second voltage and SOC relationship.

An apparatus for estimating a state-of-health (SOH) of a battery cell, the apparatus comprising:

• a memory configured to store data regarding the active fuel gauge of the battery cell based on a first voltage and state of charge (SOC) relationship;
• a sensor configured to measure a voltage of the battery cell;
• a processor configured to:
• receive a first resting voltage measurement of the battery cell from the sensor, the first resting voltage measurement measured at a first time,
• receive a second resting voltage measurement of the battery cell from the sensor, the second resting voltage measurement measured at a second time after the first time,
• receive a third resting voltage measurement of the battery cell from the sensor, the third resting voltage measurement measured at a third time after the second time,
• calculate a first difference in capacity between a first pair of the first, second, and third resting voltage measurements and a second difference in capacity between a different pair of the first, second, and third resting voltage measurements based on the first voltage and state of charge (SOC) relationship,
• determine whether the first and second differences are equal to each other and to a reference capacity difference, and
• when the first and second differences are equal to each other and to the reference capacity difference, identify an estimate of a remaining capacity of the battery cell corresponding with the active fuel gauge, or
• when the first and second differences are not equal to each other or to the reference capacity difference:
• identify a second voltage and SOC relationship having capacity differences between pairs of the first, second, and third resting voltage measurements that are equal to each other, and
• update the active fuel gauge based on the identified second voltage and SOC relationship, and
• perform a diagnosis of the SOH of the battery cell corresponding with the identified second voltage and SOC relationship.