The invention relates to a method and a device for determining the properties of a battery, in particular a traction battery. Particularly the invention determines a battery state such as the capacity and/or a charging state and/or a remaining service life of the battery, preferably with an observer and a battery model for a model-based state identification. According to the invention, a querying module for querying an operational state of a consumer supplied by a battery and a first control module for starting the determination of the properties of the battery, only when the operational state of the supplied consumer shows that it does not operate in the principal mode, are provided.