I really don't understand all the obsession with the batteries. Though
that is the part that failed, it's also the most low tech part of the
subsystem. Imho, those batteries were operated outside the data
sheet limits, otherwise they would not have failed. (Sticking neck far
out here)
The charger and monitoring systems probably have thousands of lines
of code and a vast array of electronics. Why have there been no questions
about that ?...