Hi Jeff.

Usually the battery cable is a AWG 4 wire (AWG is the ,measure unit for electrical wire diameter and is related to the maximum amperes it can handle). The AWG 4 wire handle up to 200 Amps (usually the max load of the starter on a sedan). Of course a wire with mode diameter is a plus ( then, AWG 3, 2 , 1 or 0 can be used, usually AWG 0 is used on rally cars on mu country - AWG lesser numbers imply bigger diameter). AWG number usually is printed on the plastic coat of the wire.

You can see used copper wires on good shape at naked eye, but use, vibration, contaminants elevate the resistance of the wire (no good). If you need to replace de terminal, is good time to replace the whole cable assembly.

Any battery store usually sell battery cable and terminals, on a kit or as separated items.