Parallelling two vehicles electrical systems can be dangerous, or inconsequential, or cumulatively damaging.
A cheapo pair of jumpercables, with 8 SAE gauge copper clad aluminum wire and steel clamps, cannot be compared to 4awg copper cables with a nice set of parrot jaw clamps digging into the terminal clamps/battery posts.
The worse the cables, the more beneficial it is that the donor vehicle is running, providing a higher voltage/ pressure, in order to recharge the needy vehicles battery and also provide current to the starter.
A good quality thick pair of cables basically allows one to attach a distant second battery to the first, and running the donor vehicles engine is not required.
I don't carry a jump box, but I do carry a 18 or 22 AH AGM battery that comes withing the lead acid jumper packs.
I don't trust others to properly use jumper cables, and it looks like some vehicles can't deal with the potential surges of paralleling a second vehicle's electrical system via jumper cables.
The UB12180 battery by itself, has started my 2 week cold 5.2 liter v8 engine, but in warm ambient temperatures. My starter is rated for 1.4KW output, and took nearly 1800 watts from the Ub12180 to start the engine with battery and engine at ~75f.
1800 watts divided by 12 volts is 150 amps
1800 watts divided by 10 volts is 180 amps
1800 watts divided by 8 volts is 225 amps
A cold engine and battery would cause more voltage drop and also require more amperage to turn the motor.
So one can see the higher the voltage the battery can maintain, the lower the amperaqe required to feed a starter motor.
Lower amperage means less voltage drop across the circuit
The thicker the cables, the less voltage drop there is.
The more surface area the clamps form on the battery terminals, the less the voltage drop.
Lots of variables in the cables, their clamps, and thus the quality of the circuit. Running donor vehicle's engine, revved,can make up for poor quality cables and clamps, but its better to not have to.
If time is not a factor, let the running vehicle charge the other vehicles battery for a while so that the battery acts like a buffer and voltage spikes wont travel to the Donor vehicles electrical system and perhaps fry something.