APU battery and the APU
The article fails as Magani says - but the comment added to iy by Intractable Potsherd only makes matters worse.
Essentially the APU is a gas turbine electricity generator. Once it is started it is the electrical power supply, and actually recharges the APU battery. If the APU fails, the APU battery should have enough power for required systems to fail safe, analogous to a computer UPS.
One of the APU Lithium batteries is the starter battery for an APU turbine engine located in the tail of the 787. Once the turbine (APU) is running it is generating AC to power all the systems that otherwise are powered by the main engines AC generators during flight. Part of the AC generated, either by main engines during flight or the APU when on the ground is converted to DC, which many of the systems run on. The power input or output of the APU battery is monitored, on the charging circuit, by the flight Data Recorder (FDR)
While it appears that one of the Lithium cells connected in series to form a 32v battery failed, the FDR records unexplained voltage fluctuation between 0-28v and current between 0 and 4-5 amps discharge.
It is not just a case of the the two Lithium batteries that caught fire, several charger circuit boards had failed, and had been replaced.
What occurred to me was that any anomalies in the charging circuits, or battery fluctuations, should be recorded in all the FDRs for all the 787s - all the ones that have flown and are now grounded. It is worth taking a look at all of them.