Hi. I would like to connect my dc to dc charger 50amp with the existing dc to dc charger 30amp ,I have 40ft of 4 gage wire from the truck to 5th wheel, charging 8 lithium 100 amp batteries. Do I need to run a second set of wires?
Putting 80A through that cable will generate a high voltage drop.
Have a look at a voltage drop calculator such as below. For one way distance of 40ft that is 2V drop.
Ideally you should add another larger cable. Ideally you want less than 0.4V drop.
Thank you for the information, I will add another line .