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In all of this there was only one (AFAIK) answer to the original question: "Anybody know why the negative jumper cable should NEVER be connected to the battery?"

AFAIK, it’s done to minimize the chances of a spark near the battery, where there’s the potential existence of explosive gasses.
This -^ is one reason. A very flat battery can discharge hydrogen gas. By making the connection farther from the battery you minimize chances of a spark igniting the hydrogen. This is a pretty minimal risk in my book.

A better reason:

By connecting the ground jumper cable directly to a designated chassis ground you may (likely will) created a better ground path. Connected to the dead battery, the ground path has to go through the dead battery's terminal clamp and then the car's battery ground cable. Jumper cables' conductors are often larger in diameter than the typical car's battery ground cable and therefore have lower resistance.

The order in which you connect cables can be debated forever as there are many permutations to weigh. If you have actual jumper cables independent of the 'starting device' it is always best to start with the dead-car end of the cables.

And never drop the other end of the cable one you've made the first connection. If perchance one of the connections is difficult to make without a risk of accidentally contacting something other than the intended connection then do that end of the cable first.

Last, from Gtk:

"Let the engine of the donor vehicle run at a higher engine speed."

This is a good way to risk damage the alternator on the donor car. Best to just use the donor's battery with the donor's engine switched off.

I really don't understand your post.
Wrong thread for me or you ? This thread is about jump starts as I understand , that's what i referred to. It's not about just connecting batteries .
It's in the picture and in the YouTube video.
You're right my bad. The thread title is about jumper cables. However, the initial posts describe connecting - a device - portable jump starters to a dead battery.

Both the picture and the video states the same , start with the positive cable first (battery to battery) then go with the negative but the negative goes to the depleted car's engine block or predefined negative jump start point.
Again my bad: I misread the first diagram. Yes, they are the same.
 

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Last, from Gtk:

"Let the engine of the donor vehicle run at a higher engine speed."

This is a good way to risk damage the alternator on the donor car. Best to just use the donor's battery with the donor's engine switched off.
So you are saying one should not do what the GTK manual says to do??? And also not do what people have done for years, run the donor car's engine at all??

The way people have done it for years is to set up the jump with the donor car running, start the receiving car, disconnect the cables and let the receiving car then re-charge its own battery. The donor car never "donates" for more than a few minutes.

I had one occasion long long ago where the tiny battery and alternator in my Datsun 510 could not provide enough juice to turn over a much larger engine with a very dead battery. A much larger vehicle had no trouble with it though. But I've never had that process damage the donor alternator. I doubt the GTK manual would say to do it if it was so risky.
 

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Interesting approach about not running the donor car.
This is also how I learned and did in the previous decades. Make sense not to run, not to put additional stress to the generator. Luckily never had any issue with it.
 

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This is also how I learned and did in the previous decades. Make sense not to run, not to put additional stress to the generator. Luckily never had any issue with it.
I learned to do it the wrong way as a kid. Only since I've owned and worked on Porsches have I learned that it's not the best way.

The best way to deal with a dead car battery is to fully charge it - with a charger - before attempting to start.

If you jump-start a dead-battery car, and drive away with a mostly-depleted battery you'd better drive directly to a store and buy a new battery. Very-depleted batteries subjected to the vibration and shock of being driven around have a high-probability of being damaged such that they won't hold a charge later even when fully charged.

That last bit is not my theory: I've witnessed this on numerious occasions and technical explanations exist.

If, however, is not convenient to charge the battery then...

So you are saying one should not do what the GTK manual says to do??? And also not do what people have done for years, run the donor car's engine at all??
Yup.

The way people have done it for years is to set up the jump with the donor car running, start the receiving car, disconnect the cables and let the receiving car then re-charge its own battery. The donor car never "donates" for more than a few minutes.
This is my understanding of the issue (which is subject to debate and/or correction...)

Have you ever heard that you're never supposed to disconnect the battery from a running car? The alternator is what powers the car after start up right? So why do you need a battery. The battery provides a reference voltage for the alternator and acts as a "capaciter" for transient voltage spikes that occur when various bits of the car start or stop consuming power. Without a reasonably well-charged battery the alternator can "go wild" and either damage itself or cause transient over-voltage spikes to electronics (which don't like them at all.)

A dead battery that's just been jump-started is a poor "capacitor" for the alternator.

On the other side of the cables, the running car has just started a dead-battery car's engine, and the running car's alternator is powering both vehicles, charging the the other car's dead battery, and topping-off its own battery. The 'dead' car's alternator may or may not be 'helping' depending upon the voltage it sees as a reference.

Now, when you abruptly disconnect the two batteries, the running car sees a huge change in alternator load that can cause transient voltage spikes. And the 'dead' car's alternator may suddenly go from doing almost nothing to running an engine and charging a deeply discharged battery and thus also have voltage spikes.

I had one occasion long long ago where the tiny battery and alternator in my Datsun 510 could not provide enough juice to turn over a much larger engine with a very dead battery. A much larger vehicle had no trouble with it though. But I've never had that process damage the donor alternator. I doubt the GTK manual would say to do it if it was so risky.
I think that - just like connecting the ground cable to the negative battery terminal might cause an explosion - the risk of alternator (or eletronic module) damage is probably small. The risk of alternator damage, from what I understand, is proportional to the age of the alternator (wear and tear.)
 
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