In a multiple battery setup, where is it? I've heard its good to have the ground of the second battery connected to the battery up front and all other batteries connected similarly. I've also been told that is poppycock and the best ground is the frame of the vehicle.

My thought is that even if its long, grounding to the front battery reduces the chance for ground loops and in some cases having to replace the ground after a while.

However the length of grounding to the front battery can be bad as everyone says the ground should be about 18''.

So, in a setup with two or more batteries, what would be the best way to go about grounding?

 

The best solution is a properly sized copper positive run of cable and a properly sized negative run of copper cable (multiple runs of positive and negative cable may optimize the systems transfer of power)

multiple batteries in a single location (trunk or bed of a pickup) a positive and negative buss bar is the best

these are not easy or cheep or even fully practical in many situations they are simply best

 

x2

 

I ran a 0ga from my battery to the back of the car and connected it to a Stinger 0ga T block. The second side of the T block got connected to the frame with more 0ga. The third side of the T block is my amp ground. Up front the battery neg terminal has a 0ga connection to the frame, a ground to the body, and a third to the engine.

In your case, replace the T block with the negative terminal of your rear battery.

 

So the best would be a - run form front to back, and then ground that to the frame like a typical amp ground. Gotcha

 

IMO yes. Then you have the chassis of the car AND the heavy cable in place to tag-team the ground.