Battery monitoring system comprising a secure data store and battery monitor comprising an electrical circuit configured to detect one or more electrical parameters of a secondary (or rechargeable) battery. A communications interface. A processor. Memory storing instructions which, when executed by the processor, cause the processor to : receive one or more signals from the electrical circuit, the one or more signals containing information describing the detected electrical parameters of the secondary battery. Send data containing information derived from the detected electrical parameters of the secondary battery to the secure data store using the communications interface, wherein the data is associated with an identifier of the secondary battery within the secure data store.