Actually jumping a battery that dead with another car isn't a good idea. Save that for a last option, no other choice.
A low battery will draw current in proportion to its needs and the voltage being supplied.
Using a running car or truck the voltage will be around 14 Volts if the alternator can meet the needs.
In both vehicles watch the ammeters if so equiped.
Do not continue to send 35 or more amps through a car's charging system. That can cause damage over time.
As shown here, even a moderately discharged battery will suck 35 amps or more when supplied at 14 volts.
The last parasitic draw I had was caused by a tiny nick in the jacket of my reverse light wires next to the transmission, just enough to expose the wire and it would rub against my transmission cooler line causing a short. Just came out of nowhere.
