The present invention relates to an external charger for charging a battery in an implantable medical device, comprising a coil; and control circuitry configured to automatically energize the coil to generate a charging field without initiation by a user, wherein the control circuitry comprises circuitry to periodically energize the coil to generate a first field; evaluate a parameter of the coil to determine if the external charger is possibly proximate to the implantable medical device during the generation of the first field; and energize the coil to generate the charging field when it is determined that the external charger is possibly proximate to the implantable medical device.