c) has been mitigated by putting the battery in a steel box, vented to the outside. Two batteries, well separated would provide additional security, but I believe all eggs are still contained in a single basket.
Correction, the battery
system was completely redesigned (although still using Li technology) with better control of the battery charging along with better isolation between cells (to prevent a single cell failure from propagating to the adjacent cells). The steel box provides additional protection to contain any future battery failures. Last I heard, there had been one battery failure since the redesign, it contained to a single battery cell.
The 787 has always used two separate battery systems.