You’re right Cool Guys (#893), in certification we never say “never’. Instead SCCs refer to “extremely remote” possibility. FAA Advisory Circular 25-1309 defines that as “not expected during entire operational life of all airplanes of the type”.
Or as I wrote in an article referenced earlier; “Put simply, batteries must not burn, except possibly once or twice during the lifetime of the entire 787 fleet. If batteries do overheat or burn, any fire must be safely contained within the battery enclosure and any harmful fumes must be vented overboard”.
More recently NTSB quantified the risk; “Boeing .....determined that the likelihood of a smoke emission event from a 787 battery would occur less than once in every 10 million flight hours”. In real life “there have been two critical battery events on the 787 fleet with fewer than 100,000 flight hours”.
BTW only 8 SCCs are necessary for certification. #9 Instructions for Continued Airworthiness can be developed progressively after certification.
I agree with KK, switch back to NiCads and avoid the SCCs completely.