It has taken 45 pages to get around to the safety issues rather than how to design an infallible battery.
In the end both Airbus and Boeing have sufficient expertise to design a workable system for this type of battery. The issues have always been acceptable levels of safety under the regulations.
I suspect (without the data) that the regulators were not satisfied with the level of consequential damage to parts of the system as well as the level of concern to the pilots resulting in an emergency landing.
I still await a report from the investigators specifying how and why safety of flight was impacted.