As a EE, I take note of retailers preying on lay ignorance WRT things electrical.
Like the exagerated HP specs on vacuum cleaners and air compressors, I note these things for my own amusement. I have seen jumper cables as heavy as #2 being sold, but that was, I think, at NAPA, and/or McMaster-Carr or maybe Grainger’s. I’ve yet to see anything heavier than #10 at wallyworld, poop-boys, Checkered-past, etc. The insulation will be like 1/2" OD. There will be large print saying “tangle proof, color coded clamps for safety, Heavy duty, etc.” you’ll have to use a magnifying glass to read the fine print that tells you they areonly #10 wire. Oh yes, be sure to look at how the wires connect to the clamps.
Better yet, ever seen those “booster cables” that plug between two cigar lighters? All the cigar lighters I’ve ever seen are fused at 30A. Sure, you have to wait half an hour to start the car, but, hey, no need to figure out where the hood release is.
AWG-6 cables will work noticeably better than the ASG-10 junk that are widely sold, and yes, they will start an engine directly from the “helper” battery, if that battery is in good shape, you have good connections, and the dead car’s engine isn’t really cold. I’ve carried a set of #6 cables my dad made in my SI vehicles for many years. The Diesel got a 2-0 welding cable based set. I tracked down those #2 cables I mentioned above when a co-worker became a new diesel owner and was seeking my advice…I just can’t recall exactly where we found them.
On several (4 or 5 over ~25 yrs… and I wasn’t counting) occasions, I’ve used those #6 cables to start vehicles where a jump was already set up and not working with #10 wallyworld cables. In these cases, only the cables were different…the cars were already positioned, I just swapped in my cables. This was usually met with disbelief, because these cables have fairly thin insulation, perhaps 3/8" OD…they LOOK smaller than the crap cables.
A discharged, but otherwise healthy battery will draw heavy charging current. I’ve measured 40-45A going into a not dead deep-cycle battery on my camper. That is with about 10’ of AWG-8, and return via a single vehicle’s frame. Starting batterys are designed for maximum plate area, so I would expect them to have lower internal resistance, resulting in higher initial charging surges yet.
If 10ga wire, and alternator limits the charging current to 50A, that won’t turn a cold engine, but given 10 minutes will put enough charge on a battery, that when combined with what the 10 AWG cables will supply with a 6V drop (maybe 100A?) WILL start the car.