Oh boy! Another early retiree to ponder the question "What ya do all day".
But for myself, here's what I did today.
Having finished the work on my car, I returned to my solar/lithium battery project. I knew quite early that the wiring between the multiple solar charge controllers and the battery bank was too weak. I need big bus bars connecting them, and also the 5.4kW worth of inverters.
Copper bars are quite expensive. Aluminum has 2/3 the conductivity of copper, but is a lot cheaper. Aluminum is what used in commercial installations. So, I went to an industrial metal place, and bought some lengths of 6061 aluminum flat of 1.5" wide x 0.25" thick to use as bus bars. AL 6061 has 1/2 the conductivity of copper.
For electrical connections, I will braze common grounding bars (see photo below) onto the bus bars. The grounding bars are tin-coated aluminum, and will braze very well onto the aluminum flats.
Calculations show that a 200A current will produce 0.05V drop over 6' of bus bar, or 0.1V for the two +/- connections. As the battery bank are 8 cells in series, the voltage drop will be 12.5mV per cell. This is still a bit high as lithium cells need even more precise voltage control. I will have a way to compensate for that.
PS. The aluminum bar has the same conductivity as AWG #000 (4/0) copper cable. It is a lot easier to make multiple connections to, compared to a round wire.