Remote,
The original charger (which I still have) was a trickle-only type that put out a whopping 200 mA (and, interestingly, the label also specifies an output of 9 volts). It would charge a set of 1980s NiCd batteries overnight (8-12 hours), but it would take far longer to charge any modern capacity battery (2500 to 5000 mA). Plus there is no cutoff or other battery protection. But hey, it was state of the art back then.
If I ever get NiMH C cells for my Nikko sub, I am considering making an attachment for my Tenergy charger with the proper plug so that I can charge up the batteries while still in the sub as before.
I no longer have my manual. As noted, the seals are no longer available from Nikko. My only suggestion is to keep yours out of the heat as my first replacement one got warped. I am sure you can make a decent stand - try using PVC, it is cheap and waterproof.
Good luck with your sub! Greg