A battery management system for use in charging a rechargeable battery is disclosed. The battery management system comprises a controller powered by a first power supply, at least one sensor for providing a sensor signal relating to at least one parameter of the rechargeable battery to the controller, and a data store. The controller is configured to write data to the data store based on the sensor signal. The data store is coupled to a data reader. The data reader is operable to be powered by an auxiliary power supply to read data held by the data store.