Scalf nailed it. On lithium batteries -- some even suggest having a positive/negative bus studs and then running equal length wires to each battery -- battery balance matters a bit more with lithium and this helps the batteries stay balanced. I'm not even sure this matters, but I've been in this rabbit hole, so I thought I'd share.
A few other comments:
1 - Don't buy crappy wire/cable -- copper clad aluminum is junk -- get pure copper or go up a size (or two). In my experience, USA made cable is far superior to imported stuff and I'm not a "if it isn't from the USA it is junk" type guy. Overseas manufacturing makes plenty of high quality products (even better than USA made!) -- I just haven't had good luck with thick gauge wire/battery cable.
Ancor Marine is the highest quality --- you can find good deals on it on eBay but it isn't cheap.
b) don't skimp on connections. Get high quality lugs (again -- pure copper -- or even better tinned copper) -- you can find these on eBay too.
And you should get a decent crimper. I've had good results with this:
https://www.amazon.com/p/product/B07...?ie=UTF8&psc=1
You're trying to "cold weld" your terminals to the wire... that's very hard to do with a hammer or vice, since they aren't designed for that sort of function. Temco makes a nice hammer driven tool too:
https://www.amazon.com/TEMCo-Hammer-.../dp/B00E1UUVT0
Putting your terminals in a vice and clamping them down -- or just smacking them on with a hammer isn't good enough. You're trying to avoid resistance in these connections and even if you buy high quality wire but get a crappy connection to your terminal -- you're kind of defeating the purpose of using good wire.
Sound like too much? Well it might be if all you're making is a few cables to parrallel your batteries -- so it might make sense to buy pre-made cables once your know what'll work -- but you will pay a serious premium -- so I'd rather put that towards tools that may last a lifetime.
YMMV -- 12V isn't scary or incredibly complicated -- but trying to skimp on materials for high amp loads will make your system less efficient and robust -- especially in a vehicle that bumps around on the backroads.
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