I think they expired some time ago.
You and he seem to be under the impression that the FDR has or will lose information because some battery expired. I’m just pointing out that this is not the case. As long as the unit is recovered and wasn’t physically damaged, the data will still be there. Data stored in non-volatile storage isn’t lost when the power goes out. It’s the same principal as when you power off your computer. When you turn it back on, all your files are still there.