Hows about this idea-------------Have on the seabed in certain top secret lolcations, where a D/E sub can go to with a ready charged pod of electricity so that she can recharge without the use of the diesel engines. Not unlike a jet aircraft that has to refuel in mid-air several times on a sortie. These overgrown duracell batties I'll call them could be developed to be on the underside of ships, or sitting on the seabed, I don't know, just an idea I was kicking around.
Wow…just a spectacularly naive idea…you don't know much about batteries, do you? First, the most "charge" one can hope for from one battery to another is that when you reach half charge and the EMF of both batteries are equal, well that's as far as your charge goes. You can't charge a battery "uphill" from another battery that is "downhill" in terms of stored charge. So once you equalize the charges (roughly 50%) of the two batteries, you're done. That's why a diesel is used to generate electricity to fully charge a battery- a generator can continue to supply amps over and above what is necessary to get the battery fully recharged (and really all that is happening during charging is driving a chemical conversion reaction with the electricity that when reversed will provide a source of EMF).
As far as storing the batteries on the seabed, roughly 95% of the ocean bottom is too deep to be accessed by submarines. So, you would be very limited in locations (mostly coastal waters) to park batteries on the seabed. Also, how do you keep them charged? They will slowly drain even if not tapped. And how do you recharge your storage batteries once they have been used? Also, temperatures on the ocean floor tend to be very cold, which reduces battery life and efficiency. As far as having ships provide the charges, that kind of defeats the whole purpose of submarine stealth. Plus lead acid batteries are extremely heavy and would effect the handling of your recharging ships. Also, effective ranges while on batteries is at most 200-300 miles, so you would need a lot of recharging ships operating close to the shores of a potential adversary. Also, trying to connect sources of power in salt water can readily lead to short circuits with battery explosions & fires, etc. These are the reasons why other countries are developing alternatives to batteries such as AIP that do allow propulsion for extended periods without having to run diesels.