Quote from
USMCProbe:
"The 787 APU has two starter/generators each. One powered by the APU battery, one by "something else". If ships power is available, the starter that is powered by ships power starts the APU. Taxiing in the APU battery should not have been used for APU start."
Thanks, that was the vital factor that was missing in my discussion.
The 45 amps was going into the battery, BTW, 16 minutes after the APU had started, for just 4 seconds; apparently just a symptom of the failure sequence. So, bearing in mind that the battery seems to be uninvolved in the APU start, what made the APU battery fail just 16 mins after the APU was started?
At NRT, was it used to start the APU, or did they have external power? Was it fully charged on APU shutdown at NRT? Does recharging continue from the main electrical system? If not, presumably it would have leaked some of its charge during the 12-hour flight, but not much. It seems possible that the recharge process might have been nearing completion when the failure sequence started.