[Gen.Blather]

“If you’re getting seawater in your battery compartment you’re in a world of hurt anyway, and the type of battery probably doesn’t matter much.”

I am going to hypothesize that they are in sponsons outside the sub’s air compartment and that they are in nearly indestructible individual cases. I wonder what effect a nearby explosion would have on them. Also, if they are small and hooked together each connection becomes an additional point of failure. As to charging them either a nuclear battery (a type of dry-cell except it generates charge) or a fuel cell would do a nice job.

[FreedomPoster]

They’re using diesels to charge. These are straight-up diesel-electric boats with a new battery technology, by my reading of this.

[Covenantor]

Here's photo of one Tesla battery pack, showing the tops of the Tesla mfr'd 18650 cells. Each cell is individually fused so if one or more cells go bad the remainder still function but at a reduced power level. Each cell is only 80mmx65mm, hundreds make up one battery pack. Stacking the packs in parallel and series to achieve desired power levels.