That spec looks pretty good. As said, I'd sacrifice range for more warhead, & delete the dual-activation, but I won't quibble over it.
I thought about it, but the problem is that you need a certain size battery bank, you need the proper circuit bussing and load distribution, and you need a certain essential speed of electrolyte (sea water) flowing through the battery bank to both generate the current, and cool the battery bank. The warhead is long and skinny as it is. If I make it larger, I eat into the power unit cell bank and that drops the torpedo's speed and is liable to make it run "hot".
As for getting rid of the "metal detector", I suppose I could add 50 kg of explosive in its place, but the darn thing should work since it relies on a ferromagnetic object disturbing the detector in such a fashion that the potentiometer activates the electric solenoid that, well...
Do the batteries leak gas?
Not until the seawater reacts with the anodes. You have to get the torpedo (swim out) out of the tube fairly quickly because the heat buildup in the tube will be a serious problem once the fish gets wet.
Do they require extensive (continuous?) maintenance?
The guidance package does. The gyros need to be spun up and down to make sure they do not bind and the artificial horizon governor should be calibrated to make sure the "floor" that the torpedo is set to run matches the "artificial horizon" governor gate limit. Also tail control solenoid linkages have to be tested. But we are not talking hydrogen burners and battery acid or plate pitting here, or bad things happening if you have to tilt or rotate the fish. The whole point of a slip in and out detonator module and guidance package setup is to make torpedo maintenance as safe as possible. You should be able to take off the propulsion unit and remove the nose assembly without a fire, acid spill, (no acid) or explosion at all.
Does performance vary with water temperature (or, given water activation, salinity or density)? Do they need special care (heaters or coolers) before firing? Or, worse, during non-use periods?
Wooden round but temperature, density and salinity does affect the battery bank. The torpedo will lose speed and range in cold dense less saline water. I suspect as much as 10% speed and almost 15% range off northern Japan or the Aleutians. It would be utterly marvelous around the equator.
One other drawback. It is fragile. You cannot drop this thing from a plane the way I have it currently rigged up. I'm not even sure you could roll it off a torpedo boat without damaging the battery banks which are shaped like Oreo (TM) wafer cells.
P.S. after edit. You can roll it off a torpedo boat. Speed NTE 40 knots; 74 km/h or 20 m/s. Now to figure out if a PBY or any bomber can drop it.