I assume soldering would be the best but I figured I would see what everyone has done. I am relocating the battery up front, so I have like 4-5 wires in the back (near the factory battery box, fusible link wires, 10ga or so, I dont remember whats all there to be honest) that I need to connect to the single 2/0 cable I am running up front to the battery. I soldered it years ago to the 4ga wire I had when it was in the back but after looking at it recently, it's doesn't look like it is doing so hot and I want to do this ONCE and not have to worry about it again. My idea seems a little "ghetto" to me but I was thinking use a really short piece of copper pipe as a butt-connector, get em all in there, crimp it down, fill it with solder then tape/heat shrink the crap out of it and hide it...
The stock setup had a wire from the + terminal on the battery to the junction terminal by the 500 connector. To do a remove battery setup, just run a wire from the starter battery cable terminal to the junction terminal by the 500 connector. This keeps all the fusable link sections stock and is likely the least amount of work.
Bat+ to starter lug, wire to BJT (the junction under the C-500), use 8 ga wire with ring ends, armor the wire, route it along the firewall with the C-500 chassis bundle.