For those wondering about the Cockpit Voice Recorder stopping when the airplane reverted to EMERG AC/DC power. There is a mandate for a 10 minute Remote Independent Power Supply (RIPS) for the CVR that applies here in the US to newly manufactured airplanes starting in 2010. I doubt that CP2933 was modified voluntarily to add this feature.
The flight data recorder relies on a cascade of sensors that are not reliable under EMERG AC/DC power, along with the drain to power the acquisition unit and the data recorder. Keeping in mind that the battery is needed for the continued safe operation, data recording takes too much current.
FYI, there is an ICAO GADSS initiative that in 2021 mandates an autonomous tracking system that will operate on its own power, but the jury is out whether ELT or ADS-B will be used for compliance. I am hopeful ADS-B, but it will take work to make it self-sufficient.