Not to rule out that the JMSDF won't develop their 20k tonners along similar lines, but that's the San Antonio-derived arsenal ship concept from HII, back in 2017 -
Well increased battery capacity should also give similar effect. particularly if Li-ion battery do live its hype.
The energy density isn't really there. Also there are a few different propulsion mind sets out there, a bunch of countries want to get rid of the AIP in favor of more batteries to streamline the propulsion system but the majority of nations don't really see an alternative to a dedicated AIP system.
Japanese Self-Defense Force has Bushmaster Protected Mobility Vehicles now.
Well 20-25% of surface displacement of a conventional submarine is Battery so the Japanese's sub has over 700 metric tonne of Li-Ion battery inside.
Is this really the battery's vault ?
As far as I know the fire originated from the lithium-ion battery pack. Please correct me if I'm wrong.
They are but is the cause of the fire because the battery being a Lithium Ion in the first place ?
The battery wont spontanteneously combust by itself, not without something else causing it. maybe overcharging, overheating or some design defects ? Who knows.