A charge determiner is configured to determine the state of charge (SOC) of a battery, e.g. based on at least one characteristic of at least one battery cell, and an indication of the state of charge from the charge determiner is stored in the event that the charge determiner is powered down. If the charger determiner is powered up then a substitute indication of the state of charge is provided in preference to that initially provided by the charge determiner, the substitute state of charge being based on the stored state of charge. Taking into account the stored state of charge is intended to result in improved accuracy in the initial state returned by the charge determiner and the substitute value may be used until a predetermined condition is met, e.g. based on a comparison between the substitute and actual state of charge values. In another embodiment an apparatus for providing an indication of the state of charge of a battery comprises a battery management system (BMS) and a charge determiner and is configured such that when the battery management system switches to a power saving sleep state power to the charge determiner is maintained.
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