new battery wire for 5ver plug, where to hook up?

[Sixpac2]

Hi. I have a 04 3500 Dodge cummins. I want to run a larger charging wire to my 5ver hook up plug. The stock is very small. My truck has 2 batterys. ? where do I hook up this new wire. 1) to the second battery 2) to the 1st battery 3) to the alternator ?. Do I need to have an isolator and if so what type? Do i need an inline fuse? I do not want to back draw the truck batterys. Thanks for your time. If anyone has any other ideas i would appreciate them. Thanks, marv

 

[LesStallings]

This would be a good question for the Towing, Hauling, & RV Forum