I can see that there may be an increase in current when the jump battery is disconnected, but I can't see how they would exceed the design spec.
After all, V=IR and that's constant.
Of course *that* would indicate that the current would in fact *drop* as resistance will increase by removal of the second battery, which would be in parallel to the car's and therefore would cause a smaller resistance and therefore an greater current for the same voltage. I'm thinking that something is amiss there, however, since I would *assume* the jump battery is adding energy to the system, while the car's battery is absorbing energy to increase it's level of charge. Or of course, it could be increasing the drain on the system as it will *also* be recovering to its maximum level of charge, having given up energy to start the car.
So, not at all simple. I've been looking for a long time for someone to explain the physics about why jump starting is such a bad idea. Not found anyone yet. Even then 4200 manual says it's allowed.
My strong suspicion is that it's been discouraged by car manufacturers simply cos too many people get it wrong, and then fry something. Which is a rather different thing.
Always willing to learn though, as I'm *sure* someone must know.
Mig welding I can see for sure: Many volts
C