A trainer cassette unit 101 for use with an auto-injector having an electrically powered drive unit comprises a trainer cassette unit housing 120 defining a cassette unit housing cavity and a forward projection aperture. A removable cap 150 fits over the cassette unit housing thereby acting to close off the forward projection aperture of the training cassette unit housing. The training cassette unit housing is further provided with one or more first engagement features 125 arranged for reversibly engaging one or more second engagement features 125 provided on the removable cap. A shuttle lock control 132 provides one or more blocking elements 134 for selectively blocking movement of the one or more first engagement feature relative to the one or more second engagement feature, thus enabling the removable cap to be locked to the cassette unit housing. The trainer cassette unit further comprises an identifier 121 that identifies the trainer cassette as being for use in training operations. The identifier may be an RFID tag that can be read by a drive unit of the auto-injector to identify the training cassette.
