this is very interesting from DeepInfar, AKA the underwater DJI.
These power modules, can power AUVs or gliders at Ocean floor pretty much. That would make UUVs very hard to detect.
btw, this is just the thruster. You can theoretically have fuel cell generate electricity to power something like this. Doesn't have to be all battery powered.EuroAtlas is proposing something similar for their Greyshark UUV. However, service interest is very limited, from what I am told. They are far more interested in the fuel cell variant which carries more power/storage onboard.