Scenario facts: a piece of stranded copper battery cable about 3.5"
long with two soldered connectors at each end, used for ground
connection on a motorcycle battery. The cable broke in the middle with
what looks like a stress fracture. Cable was flexed many times, every
time battery had to be taken out or when battery had to be disconnected
for electrical tests or electrical modifications to motorcycle wiring.

Son contends it is the fault of soldering connectors onto cable, which
heat stressed the cable. I think it is copper work hardening when
flexing cable, thinking that heat if anything (maybe to low) would help
anneal copper.

Your opinion welcome.
cheers
T.Alan