Apologies, deleted that post because it should have been sent to tech log as
a follow up to a previous post
cwatters:
They must have some sort of diagnostics internal to the charger / monitoring and
data would ideally be stored locally. The fdr only has limited storage capacity,
but a subset of that data, say bus voltage and any fault codes, might be sent to
it as well. If the data from the charger / battery is lost, the limited fdr data
may be the reason why we have only been told thus far that a battery over charge
condition didn't occur. The fdr data may be the only thing they have at present.
pax2908
As for the thresholds, they would be set below cell voltage and temperature
limits. If the charger is really smart, it should also be able to predict cell
failure before it causes a problem, by comparing known good cell characteristics
against data from individual cells over time. Where data logging is used, it's
normally stored to non volatile memory within the subsystem. Often flash memory,
much like you would find in a usb memory stick, but manufactured and qualified to
a much higher specification.