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Your lithium batteries will be trying to pull a lot of amperage over the 7-pin, more, much more, than a lead acid battery would, and trailers are designed for lead acid batteries probably only as was the truck's wires. Lithium will pull more amps than lead acid.
5ers typically have a very long wire run as the wire comes out of the rear of truck then up to front of the trailer, not a very direct route. Long DC runs are bad.
Alternatively, there is probably a fuse on that wire you can simply just pull out if you do not want to do any work.
You should be able to leave your 7-pin plugged in while stopped. Unless your 7-pin is a do-it-yourselfer install where they hacked the trucks rear lights and/or 4-pin trailer plug to make wiring for the 7-pin, then as mentioned ,if it is factory installed, there will be a relay that turns off when your truck turns off so there will NOT be any electrical connection between your truck battery/alternator and your trailer anyway.....
0truck0 had a lot of good comments in that post, but I add this 'reply' to clarify his guess at the amperage over the 7-pin interfacece.
He is correct that nearly all fctory installed 7-pin interaces will only enable the the "Trailer Battery Charge" wire connection when the truck ignition is turned to at least "accessories". But some aftermarket installers may not have done that. He is also correct that you have the option of pulling the "TBC" fuse when you want to disable the truck battery connection, that will work even if the TBC wire doesn't go through an ignition-sitch managed relay. That fuse is probably inside the under-hood fuse box, but could be located under hte the dash board as well.
My complaint with 0truck0's post is his claim that "Your lithium batteries will be tryng to pull a lot of amperage", that part of his post wasn't correct. Lithium batteries, when not fully charged, don't actually PULL amperage at all - they only ACCEPT it, while the voltage on their terminals is high enough to push power into the batteries (and while BMS limits allow charging to occur).
When current into the batteries begins to occur, resistance within the wires along on the "long DC wire runs" causes the voltage difference at the battery terminals to fall. The amount of "voltage drop" varies according the amount of current, the wire sizes, and the wire lengths. (There are online calculators which you can use to create estimates.) In this situation, the running truck will have about 13.5 volts under the hood. If the coach batteries are all the way down to 20% state-of-charge, they will ACCEPT at least some charge current input until the voltage at their terminals falls below about 12.9 volts. But what is the maximum current which the wiring will allow, before creating too much "voltage Drop"?
If we assume a wire size of 10-AWG and a one-way distance of 40 feet, with source voltage of 13.5 volts, the end voltage will become inadequate to supoort higher levels of charging current at about 6 amps. Bigger or shorter wires could allopw for more current, buy you will not be able to charge those batteries at a higher rate - unless you add a DC->DC charger/converter unit.
The change to Lithium batteries wil not "pull a lot of amperage" when the wiring creates a lot of voltage drop - and the wiring will do that, unless you increase the wire sizes ($$$$) or add a boosting converter/charger unit.
