Hi,
EEngr:
First, think about the volume of raw data that could be collected from the internals of each subsystem. The FDR architecture would have to be revised significantly. And since that is a certified part of a production aircraft, backing down to the 'standard capability' FDR would require recertification.
Carefully selected TEST POINTS. E.g. Pitotīs, AoA vanes, cell voltages, etc. Limited data. Optimized by "caching" more data inside important boxes. Actually this is being done
(QAR). (for other purposes)
Second: The internal charger/battery data is taken from the same sensors that drive the charge controllers. So if these are faulty, so too is the recorded data. Faulty data might tell investigators something. An anomalous zero cell voltage reading may indicate a broken sense lead for example. But at what point do we stop incorporating redundant sensors into systems just to satisfy these enhanced FDR requirements?
Itīs VERY EASY to have a NEAR PERFECTION probing for all cells inside a Li ion batt case. LOW COST!
If this info were recorded NTSB and JTSB VERY PROBABLY long ago reported WHY both batteries (JAL and ANA) failed.
How many bits/bytes for this? Easy to have ALL REQUIRED info on cell voltage in less than 1MB. Yes! ~ 8 M bits. I could reduce, if necessary further.
PS
Cache inside batt case operating like a CVR. If crash, stops recording and make available it to aircraft FDR. Redundantly stored in cache AND FDR.