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Discussion Starter · #1 ·
In the owner's manual - about page 6-11, if close to mine for 2015 year - they describe the battery boost method.

5. Start the engine of the booster vehicle and
let it run for a few minutes.

6. Keep the engine speed of the booster vehicle
at about 2,000 rpm, and start the engine
of the vehicle being jump started.
I've had two vehicles in the past where my alternator died within 2 weeks of boosting someone this way. Years later, a guy I know with some mechanical know-how said the load put on the booster vehicle's alternator during a dead vehicle boost is too much for it and causes premature failure. So I've avoided running the vehicle in the booster since hearing that. I just hook up batteries and work from that, while keeping the booster's engine off.

I know there is a lot more current produced by the method described in the manual, and I've had good results for the other guy needing help, but not for my booster vehicle.

Are there any mechanics or engineers that want to add an opinion to this?
 

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If your jumping with a running vehicle, as soon as the second vehicle starts you have two alternators, two batteries and who knows how many loads, all running in a single parallel circuit. Anyone that tells you they know how that particular circuit will behave, especially with modern ECU controlled charging systems - is lying.

If you must boost someone with your vehicle, I would go so far as to completely disconnect the good battery, boost the second vehicle, and immediately disconnect my battery from it.

Better answer is to carry one of those cheap car boosters you can get now for like $100
 

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I‘ve never had an alternator fail after jump starting another vehicle.

The reason the manual says to start the booster vehicle and let it run a few minutes is so that the good vehicle will charge the dead battery some so that by the time you try to start the dead vehicle that battery is carrying some of the load and not your battery/alternator, in theory.

I’d say there was another underlying cause of your alternator failures. Maybe an already weak and failing alternator, or maybe a short in the vehicles you were boosting. Which is why I like @Lowcountry idn ’s advice on disconnecting the good Battery, or just carrying a good lithium jump pack for such occasions so as not to risk your vehicle by boosting someone else’s.
 

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maybe a short in the vehicles you were boosting
IMHO, this is the issue with most vehicles with a dead battery. If your battery goes dead while your out and about, it likely means either your battery has shorted or your alternator has died - or some other electrical problems. Modern cars don't let you leave your lights on anymore , the BCM turns them off after some period. So they usually die for a reason. Why connect your working system to that if you can avoid it.
 

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Discussion Starter · #7 ·
I don't think a detail is always noticed in what I wrote. The alternator does not fail on the spot. One or two weeks after the boost, it seizes up. Once boosting from a Tacoma and once boosting from a Maxima. Neither vehicle was very old.

It's like it accelerates the wear and tear. People often say these components are made very small these days and they generate a lot of heat, which eventually kills them, so the extra load is contributing to that.
 

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i have jumped many stranded motorists and neighbors. I always leave my truck running, hook up my jumper cables to my battery, then connect them to the dead battery, let it sit for a few minutes while idliing my truck at 1500-k rpms, then have the other driver start their car, then immediately disconnect the cables from their vehicle.

I have done this many times with not just my X, and its never created a problem. not with the alternator at least, I could see the argument that that is why my batteries keep dying after about a year or so...but i really dont think its related.
 

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Had a frontier at work that jumped hundreds of vehicles. That was one of the main purposes of the truck. Go jump start cars that sat in the parking lot for too long. Many were totally dead. Running engine on the truck was the norm. Never once lost an alternator.

You just had bad luck a couple of times.

Siezing alternators is a bearing issue anyway. Nothing to do with spike electrical loads.
 

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The only times I've killed an alternator on my cars is when the driver of the "donor" car didn't follow these procedures. They just connected, had me start, and disconnected. Lost about 4-5 alternators (mostly GM) this way. I use the method above with both cars running for about 10 minutes after start. Never had an issue with either car. I still prefer to use jumper cables and 2 cars, but I keep a jumpstart pack just for emergencies (this one has a "boost" feature that's supposed to give the battery some extra charge before starting).
 

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At the risk of being slightly off-topic, I pause to laugh at the anemic picture-hanging wire that OEMs include as 'jumper cables' these days.
 

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Discussion Starter · #13 ·
The only times I've killed an alternator on my cars is when the driver of the "donor" car didn't follow these procedures. They just connected, had me start, and disconnected. Lost about 4-5 alternators (mostly GM) this way. I use the method above with both cars running for about 10 minutes after start. Never had an issue with either car. I still prefer to use jumper cables and 2 cars, but I keep a jumpstart pack just for emergencies (this one has a "boost" feature that's supposed to give the battery some extra charge before starting).
I was ready to side with the opinion that my experience with dead alternators was a coincidence and now you back it up.

I don't understand the difference between "these procedures" and "connected, had me start, and disconnected". What can be done wrong within the steps of connecting, start and disconnect? The only detail I can think of is the order of connecting the terminals, but I fail to understand if that's what you mean or why it can matter.

The only risk I'm aware of with connection order is sparks in presence of hydrogen as the battery is charging up, or shorting out the cables if you just left two from one end on the ground and touching each other.
 
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