Originally Posted by Smithyyy
Struggling manfully back to the topic - re charging from the car. A caravan socket (either a13 pin or a second 7 pin (7S) socket) gives a choice of a permanent or an ignition-switched 12V supply, designed for charging caravan batteries. So fitting one of these and as someone says above running the lead to a high current (DIN) socket on the boatto supply the battery(ies) is a neat way of doing it. I tend to think of it like recharging a flat car battery after a jump start - running the car for half an hour or more seems to do the trick
Check out carefully what type of wiring your car needs, modern electrics don't like extra wires just spliced into the loom, fouls up bulb failure sensors ans potentially much more complex stuff that runs trailer sensing, multiple bulb operation,etc.
You really want a bypass relay anyway in the wire to the boat so the connection only completes if the car is providing power -otherwise you risk the car trying to draw current from the boat
Potentially, yes, but ... unless the OP is qualified and/or experienced could be a nightmare wiring it in or it would need the services - and costs - of a professional. Twin boat batteries, high current sockets, bulb failure devices, bypass relays, switched ignition feeds
et al...and after all that, you still don't know what state the boat batteries are in when you start the car journey or when you finish it.
Too many unknowns and risks for me to be heading out sea with.