Hello,
In my ROV, the batteries are in a separate tube. I want to put a female jag on the penetrators I use in this tube. In this way, I can charge my battery without connectors and protect my cables under water. However, the inner diameter of the capped penetrators is 4-5 mm and I cannot find the female jag suitable for it. What are your solutions to connection problems?
Your question is interesting, but I don’t quite understand what you’re asking. What is a jag?
I am sorry no jag. I try said jack 
I haven’t found a small connector or Jack that has a high enough current rating to run the vehicle. Also, I monitor the batteries cell voltage when charging which requires an additional 5 conductors so the only solution at the moment is to remove the battery to charge it.
Also, while you’re charging the battery in the housing you can’t use the vehicle. It’s easier to recover the vehicle when the battery is getting low, swap it with a charged battery, and charge the flat battery.
I use a BMS with balance circuit to charge the battery, so I just need the (+) and (-) poles. I also set my charge current to 2 or 3 amps. I just need a stereo jack to go into the 4 + -0.5mm hole.
these may work for you:
They have a dummy plug you can use when done charging
Thank you.this worked very well for me.