A tale of battery cables

I guess it depends on many factors. I have found in 45+ years of soldering wires, that with vibration and age they fail just past the solder.
I'll 2nd this... I soldered connections in may early rally cars but stopped after they started breaking right where Kit says. If you solder connections, you have to solidly support the wires a few inches past the end of the solder to prevent this problem.

BTW, the conductivity of solder is right around 1/10th that of copper.