For rigid electrical connections, copper busbars offer a very efficient solution. Resistivity in copper bars is very low, .25 in^2 bar 1 foot long is only 0.0000329 Ohms - roughly 8 Watts lost at 500 Amps.
Where to use them:
Very rigid high power connections.
Connection of Field/Armature on Motor Terminals
Where not to use them:
Anywhere that needs flexible connections.
Between battery terminals. (May cause undue stress to terminals.)
Silver, tin or nickel plating for copper busbars is necessary in high temperature applications. At DC to 60Hz there is some controversy as to which plating is the best because while silver has the highest conductivity, it is also more noble than copper so it will actually accelerate corrosion wherever the plating gets scratched. Thus, you don't want to just use toothed lockwashers, for example, in between a nut and the bus bar (i.e. - use a flat washer, too).
Tin plating is an excellent solution practically speaking, because it protects the copper, has reasonably low resistance (higher than silver or copper but lower than nickel) and can be easily applied yourself using "electroless" plating kits such as "TINNIT".
Epoxy Powder-Coated Busbars allo for closer element location in a system, which is excellent for single conductors or multiple conductor assemblies that can have countless forms. Epoxy powder coating is also well matched for insulating thick conductors, as well as conductors with multiple electric contact points. The material also has a high dielectric strength and is a sturdy insulator, immune to most elements.
Tin (non-lead bearing) solder can work, but it may sweat at a higher temperature. Having someone with a hobby plating set-up will make it work better. Alternatively, buying a hobby plating transformer and some acid and cyanide will provide you the ability to do it at will. Nickle is the metal of choice. It is used to 'flash' the copper bar material, prior to plating with silver, and thus prevent corrosion by 'sealing the surface of the copper. Then fine silver is used to do the final plate, but the copper is a naturally oxidizing metal, that is why it is noted for its 'green patina' and why the planet Venus is considered the Goddess of Copper. If it is just straight plated with silver, it would be useless as the corrosion will start and the bar will blister with copper oxide and shed the silver. Nickle and silver don't melt like tin will at a temperature under 1000 degrees. (Nickle = @1100 deg f, Silver = 1470 deg f)
If you have access to a good metal cutting blade and jig-saw or a scroll-saw with a metal cutting blade, buy a sheet in the desired thickness. It's cheaper and you can customize your needed 'bar'. You can then also use a propane torch to 'anneal the copper to work or bend it. A hand drill with some good sharp bits will always provide good puncturing capabilities for necessary holes.
Several companies offer standard copper busbar designs in stock stock, ready to ship. This may be a good alternative for the DIYer who is not comfortable with the steps outlined above.
If using it for battery terminals, make sure the batteries are well secured and the battery boxes are solid so that the batteries do not shift around or flex relative to each other during driving. Favor a bus bar that is fairly thin but wide (to get enough conductivity) and design them with "kinks" in the middle so that they can allow slight movement between the batteries.