I bow to others knowledge of naval systems but I’d like to back this up and comment on the general unfeasibility of replacing a crewed SSN or SSK completely with a solely battery-electric SS (SSE?) or AUV. The physics simply doesn’t stack up.
The Collins/Attack/AUKUS saga has highlighted that range is a critical factor for RAN subs. To get range a sub needs to be powered either by something where the fuel doesn’t run out (nuclear) or carries enough fuel to burn to provide the required amount of energy needed to reach the range provided (Diesel) or stores the energy directly (battery). In all three cases the sub also needs to contain the crew, weapons, sensors and the engines that will take that energy and convert it to forward movement.
So the rate at which energy can be stored is critical. The more dense the form of energy storage, the further the sub can go for a given fuel storage space. The following are theoretical maximum energy storage density in Mega Joules (MJ) per litre of volume for various sub power options:
Lead battery 0.5 MJ/L
Lithium battery 4.3 MJ/L
diesel fuel 45 MJ/L
Uranium U235 3,900,000 MJ/L
Clearly, even the most efficient battery is ten times less efficient in energy storage than diesel fuel. Nuclear power is one million times more efficient. There is simply no way a submarine or UAV powered by battery alone will travel as far, or as fast, or carry as much as a similar sized SSK, let alone SSN. Some things engineering and research can resolve over time. But not basic physics.