Re: Extinguishers...
Any other battery would be better for this sort of application than LiIon, which sacrifices a level of stability in exchange for increased energy density. At this scale, energy density is less of an issue, but LiIon has become the meme thanks to Mr Musk's marketing.
IMO grid-scale storage is a dead-end anyway; it's only being pushed to try and paper over the problem of renewal intermittency. Regardless of one's views on renewables, a lot of the issues that these storage sites are supposed to fix would be better resolved with HVDC interconnects than with grid-scale storage. Energy storage, if it's required, should constructed at end-points, where it can be tailored to the needs of the consumer, whoever they might be.