@EEngr
Unfortunately, I suspect that once Boeing gets the fireproof box solution certified, the battery problem will be put on their back burner (figuratively).
I expect Boeing won't be in a position to wipe their brow and sit back and relax.
The failure rate of batteries once returned to service will need to return to the one-in-a-billion chance per flight hour as I believe that is the certification requirement.
Also, as it appears a failure of the APU battery triggers a failure of the APU, if the APU battery keeps failing at what is considered too high a rate, the 787 will not be able to be certified beyond ETOPS-180 and that is going to cripple it with operators like QF, NZ and others who were planning ETOPS-240 or ETOPS-330 missions.