The killing reason why most JumpStart cables can't jump-start a car is that copper-clad-aluminium (CCA) wires are used. CCA is a mixture of copper and aluminium. At TRIKIT, we manufacture our JumpStart cables with 100% pure copper wires (no aluminium).
Why is CCA not good? because aluminium has low melting point and high resistance. Hence, it causes heat much faster during a jump-start, the wires then melt due to its low melting point. Besides, too much heat will cause the rubber of the cable to melt or catch fire.
I believe this is quite straightforward. Thin cables do not have enough capacity for sufficient electricity to flow through for jump-start.
*Beware that the rubber portion is thick but copper wire portion is thin. Some sellers deceive the consumers in this way.
3. Size of battery clamp (head)
Thicker and bigger battery clamps are better for electrical flow. Steel is enough for this part.
*Beware that some sellers deceive by electroplating the battery clamp (head) with copper so that it looks like copper.
4. Fully-covered battery clamp (head)
For safety purpose. Most JumpStart cables in the market do not meet this requirement.
TRIKIT - "Why buy cheap and low quality car emergency products & RISK YOUR LIFE when you can have high quality ones at reasonable prices?"