A method for operating an external medical device such as a defibrillator includes obtaining a data set from a battery pack and examining the data set to determine whether the battery pack is authenticated for use in the external medical device. If the examination does not confirm the authentication, the method includes causing the device to follow a non-authenticated battery pack protocol. The non-authenticated battery pack protocol may include drawing power from the non-authenticated battery pack only if it is the only available source of power for the external medical device. It may include limiting functionality of the external medical device. It may include modifying the battery status information display for the non-authenticated battery pack. A power system for an external medical device may include a power source external to the medical device and including a memory which stores data indicative of an authorized status of the power source and a processor in the medical device configured to analyze the data and to control a function of the medical device based at least in part on the authorization status.