Methods, systems, and computer programs for managing authentication data for an authentication device are disclosed. An authentication device may be included, for example, in a mobile device battery so that the battery can be authenticated by a mobile device. In some implementations, encrypted certificate data are stored on an authentication device. The encrypted certificate data are accessed, and unencrypted certificate data are generated by decrypting the encrypted certificate data. The unencrypted certificate data are stored on the authentication device. The unencrypted certificate data enable the authentication device to provide a valid reply message, for example, in response to receiving an interrogation message from an interrogation device. In some implementations, the reply message includes the unencrypted certificate data and a response value generated by the authentication device based on a secret value.