Number of Batteries in Japan's new Taigei submarine.

More than the 640 likely LIB battery modules on Taigei and the Soryu Mk IIs (Oryu and Toryu) is possible, although evidence on this is not definite. Maybe 3 x 240 = 720 in bottom decks is possible. Twice as many batteries 2 x 480 = 960 is less likely if double decks are required.

According to several sources, including Janes (October 14, 2020), Japan’s new Taigei class submarine will have almost identical dimensions/displacement (length 84m, beam 9.1m, draught 10.4m, and standard [surfaced] displacement of about 3,000 tonnes) compared to Soryu Mk I and II class’s (84m, 9.1m, 10.3m, standard displacement of 2,950 tonnes). The main change will be/is replacement of the Soryu Mk I’s AIP (Stirling engines, Hydrogen and LOx tanks) with more batteries in the Oryu, Toryu and the Taigei class. But how many extra batteries is not publically known.

So the almost identical Soryu/Taigei dimensions/displacement means the Taigei class represents a something for something switch rather than the usual larger submarine class replacing its predecessor.

In the Table at https://gentleseas.blogspot.com/2017/03/comparison-of-soryu-modes-of-electrical.html Anonymous indicates:
-  Soryu Mk Is have 480 LAB modules and
-  Soryu Mk IIs [ie Oryu and Toryu and presumably the Taigei-class] may have 576 or 672 LIB modules
   [or some number in between]

Here https://gentleseas.blogspot.com/2017/05/first-picture-of-libs-and-labs-for.html Anonymous indicates dimensions and weights of modules are:
-  LAB is 444mm x 432mm x 1,665mm and weighing 880kg, and 
-  LIB is 444mm x 431mm x 1,647mm and weighing 770kg

If accurate this demonstrates that LAB and LIB battery modules for Japanese submarines are of similar dimensions and weights. It is likely Japan would not drastically increase the number of modules.

For example, even when Soryu Mk I’s AIP (Stirling engines, Hydogen and LOx tanks) are removed Japan might not double the number of 480 modules to 960 (in a Soryu Mk II (Oryu and Toryu) or Taigei class) submarine as this may make the submarine too heavy and take up too much of a submarine’s space/volume.

Also, as Anonymous advises, a double deck arrangements (if used) is unstable in terms of top heavy balance/buoyancy and increases “stray magnetic fields” see paragraph [4] at http://gentleseas.blogspot.com/2020/10/electrical-propulsion-costs-soryu-mk_5.html. So it is more likely Japan has maintained a single deck, “all on bottom” arrangement. 

As there are electrical power/engineering and measurement/slot advantages of having a simple multiple of batteries of the same size then exactly one third more than 480 modules of the 444mm x 432mm LAB measurement equals 640 modules of the 444mm x 431mm LIB measuement on Oryu, Toryu and Taigei.

If/As the LIBs are slightly shorter at 1,647mm they can fit into the LABs 1,665mm slots. This may also allow some space for active and/or passive heat dispersal and fire suppressant fittings for the LIBs (if needed). Also if the LIBs weigh just 770kg compared to each LAB’s 880kg that is another reason (in addition to AIP removal) that more LIBs can fit – in terms of not increasing the Taigei class’s weight unduly. 

Supporting the 640 LIB module estimate is Japan’s defense agency ATLA's lists of central procurement items. “SMC-8B specification” p.9, part translated at http://blog.livedoor.jp/wispywood2344/others/SMC-8B%20P_9_s.png which indicates the [submarine] “is powered by 2 groups of battery modules, each consisting of 320 battery modules...” ATLA’s lists suggests this battery specification of Taigei is the same as Oryu and Toryu ie. 640 battery modules.

More than 640 battery modules is possible, although there is less definite evidence of more than 640. Twice as many batteries as the 480 in Soryu Mk Is is unlikely for the reasons stated above. Maybe 3 x 240 = 720 in bottom decks is possible. More evidence for these numbers, which may appear in months or years, is needed.       

Of interest is ATLA’s current listed research activity - as at October 19, 2020:  "Conduct research on electricity storage system with large capacity and high density, electricity supply system with high efficient and compact sized to extend submarines’ underwater endurance without increasing ship size." (Diagram and caption courtesy ATLA, October 2020, at https://www.mod.go.jp/atla/en/soubi_kansen.html).
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