@Helix Von Smelix
In the industry that I work in, if we have a failure of unknown cause, when we get to a solution, we would have two test rigs setup. One with the modification, and one to the previous standard.
If under duplicate testing neither fails, we do not have a fix. We would have to ensure the old design fails, and the new design runs as required.
I hope Boeing is confident with the testing, and solution.
Once the NTSB and JTSB have identified the root causes of the battery failures aboard JL8 and NH692 I fully expect we will see new Airworthiness Directives issued to specifically address them.