A battery system, comprising: - a battery configured to be coupled to an electrical system; - one or more sensors configured to measure battery parameters during operation of the battery system; and - a control module communicatively coupled to the one or more sensors, wherein the control module is programmed to: - determine a first estimated state of charge of the battery using a first current integration process, based on a first estimated capacity of the battery, an initial state of charge of the battery at the start of a current integration period, and current indicated by the battery parameters measured during the current integration period; - determine a second estimated state of charge of the battery using a second current integration process which is parallel to the first current integration process, based on a second estimated capacity of the battery which is less than the first estimated capacity of the battery, the initial state of charge of the battery, and the current indicated by the battery parameters measured during the current integration period; - determine a third estimated state of charge of the battery based on a first Kalman filter using the measured battery parameters; - determine an actual capacity of the battery based at least in part on the third estimated state of charge when the second estimated state of charge and the third estimated state of charge are both less than the first estimated state of charge or the second estimated state of charge and the third estimated state of charge are both greater than the first estimated state of charge. - a battery configured to be coupled to an electrical system; - one or more sensors configured to measure battery parameters during operation of the battery system; and - a control module communicatively coupled to the one or more sensors, wherein the control module is programmed to: - determine a first estimated state of charge of the battery using a first current integration process, based on a first estimated capacity of the battery, an initial state of charge of the battery at the start of a current integration period, and current indicated by the battery parameters measured during the current integration period; - determine a second estimated state of charge of the battery using a second current integration process which is parallel to the first current integration process, based on a second estimated capacity of the battery which is less than the first estimated capacity of the battery, the initial state of charge of the battery, and the current indicated by the battery parameters measured during the current integration period; - determine a third estimated state of charge of the battery based on a first Kalman filter using the measured battery parameters; - determine an actual capacity of the battery based at least in part on the third estimated state of charge when the second estimated state of charge and the third estimated state of charge are both less than the first estimated state of charge or the second estimated state of charge and the third estimated state of charge are both greater than the first estimated state of charge. - determine a first estimated state of charge of the battery using a first current integration process, based on a first estimated capacity of the battery, an initial state of charge of the battery at the start of a current integration period, and current indicated by the battery parameters measured during the current integration period; - determine a second estimated state of charge of the battery using a second current integration process which is parallel to the first current integration process, based on a second estimated capacity of the battery which is less than the first estimated capacity of the battery, the initial state of charge of the battery, and the current indicated by the battery parameters measured during the current integration period; - determine a third estimated state of charge of the battery based on a first Kalman filter using the measured battery parameters; - determine an actual capacity of the battery based at least in part on the third estimated state of charge when the second estimated state of charge and the third estimated state of charge are both less than the first estimated state of charge or the second estimated state of charge and the third estimated state of charge are both greater than the first estimated state of charge.