Jump starting cars

I am used to carrying jumper cables. I hear a lot about how they are obsolete. Is this just because if you do something stupid like
hook it up backwards, the consequences are worse? Or is there something fundamentally wrong, now, with using cables?
I am thinking about replacing cables with these devices. You might want to comment on the safety of using cables with these cars
(various family members):
2014 T Avalon hybrid
2011 Honda CRV
1999 Lexus ES300
1999 Lexus LS400
2007 Dodge Nitro
2015 Mazda 5

Are at least the 1999 models safe with cables?

Are there any “best brands” of the small portable starters?

thanks in advance…

I realize that wasn’t well written. I am thinking about the new small Lithium ion portable car starters, which seem to cost around $100

Don’t jump the hybrid, if it won’t start it’s the main battery, not the 12V battery. If the 12V battery is dead, jumping won’t help (at least it didn’t help me).

Jumper cables work great as long as you can get to the battery. Positive to positive. Negative to battery negative of the good battery. Negative cable on bad battery car goes to chassis ground away from the battery. Hydrogen gas from the battery is the dangerous thing you want to avoid and is why the last connection is away from the battery.

I know how to jump cars. The question is how are new cars different.

New cars have many expensive and sensitive electronic components. As long as you jump start them correctly you should have no issue. Hook up the cables backwards and you will get a very expensive lesson. I have jump started several cars with my 2014 Mazda6. I use extremely heavy duty cables and safety glasses while following knfenimore’s instructions.

You can jump all but the hybrid. It has the 12v engine battery and then the hybrid battery. I don’t like the battery packs. They sit in the trunk and are dead when you need them. They don’t provide the current that good cables do and the batteries don’t last but a few years.

When you’ve hooked up two cars in parallel like that, the batteries effectively bridged, the voltage regulator in one car may be trying to achieve a different voltage than the regulator in the other car. One car may think the voltage should be 13.0 volts and the other car might think it should be 13.5 volts. So the two will fight each other.

In older cars the voltage regulator was pretty much a stand alone system. And since folks jumped their cars all the time without problems, that pretty much proved the fighting voltage regulators wouldn’t ruin anything. But in newer cars the computer takes charge of this voltage regulator function too. Now you got the cars voltage regulators and computers fighting with each other. One will be trying to make the voltage go up, the other down. And it is hard to say what will happen.

You are right to be thinking that some cars may need special handling.

What do the owners manuals say about jumping the cars in your list?

Probably some of those cars are not sitting in your driveway all the time. You would find your answer - and do your family members a favor - by having them read about jump starting in their manuals, and tell you what they found.

You are indeed right to be thinking some cars may need special handling. GeorgeSanJose is right that running two cars bridged in parallel is asking for one of them – usually the good booster – to fry its alternator. Rule of thumb: (1) Connect the two cars as per knfenimore’s directions. (2) Run the booster to charge the boostee’s dead battery for “a few minutes” (3). Turn off the booster. (4) Crank the boostee.

If “a few minutes” were adequate, the boostee should start right up. If it doesn’t, then either a few were too few, or there is something else wrong with the boostee. In no case should both cars be running at the same time they are bridged with the jumpers. Observe step (3): keeping the booster running while cranking the boostee worked fine back in the sixties.

But the sixties are over.


“In no case should both cars be running at the same time they are bridged with the jumpers.”

No kidding

If both cars were running, then none of them needs a jumpstart

I could not resist

I hope you’ll take this as good humour


I guess this is the second similar thread over the past few weeks. I always have jumper cables with me when traveling. Have used it without problem in newer cars, but that is like claiming you can drive over 100 MPH without getting a ticket.

How about using the good car’s battery but disconnecting the leads or at least the +ve one. Wouldn’t that exclude the electronics on the good car?

By the way OP, you have quite a few cars. Putting a charger in all of them will become costly.

I think that a lot of jumper cable starting problems could be avoided if the people involved would have a little patience instead of connecting the cables and then hitting the key.

Allow the engine to idle for 10-15 minutes at least before attempting a start. Unless the battery is flat gone that should be enough time to build the dead one up a bit and prevent any problems.

Disconnecting the good car’s battery will indeed protect the electronics of the good car, and is the surest way to do so. But it also disconnects the (allegedly) good battery from the dead car. That good battery can add significant current to the boost with good cables and connection. So I leave the good battery in the circuit and just turn off the good car’s engine before cranking the bad one. Disconnecting the good car completely is the surest protection, but if the bad car doesn’t start and you want to try again, you need to re-establish the connection – always an iffy procedure. And sometimes the bad car really does have a really bad battery that won’t hold a charge at all even for a few minutes – then the good battery is the only one available for the boost, and must remain connected.

(This happened to me a few years back. 10-year old Camry stalled in left lane, finely-dressed lady fresh off the boat from India was frustrated, she’d just bought the car and it was all she could afford. Looked like the OEM battery, and it was dead, Jim. I took my time, followed the above procedure, explained what I was doing and that no, a ten-year old Camry is not a lemon, but a ten-year old anything will have maintenance issues, brakes, shocks and struts chief among them. And batteries. Firmly suggested she not turn off the car until it was safe in her driveway, that of a battery shop, or of the dealer that sold her the thing as it was still within the 90-day comprehensive used-car warranty covering everything 'cept parts and labor. He’d almost certainly spot her another battery, though it may or may not be an improvement.)

Point is, like I said, prevention is a lot easier. Kinda like carrying a can of gas in the trunk in case you run out. If you don’t let your tank get too low, you won’t run out. If you replace batteries at four year intervals or at least have them tested, you likely will never need a jump. If you do such as at frigid temps or mistakenly leaving lights on, you’re probably going to need a truck anyway and all of your computer learned settings will be gone. Jump starting these days should be a very rare event.

Since we are on batteries, I will tell my recent experience.

Got home late, heard a hissing noise in the garage and sure it was a flat. Thank god for the old school full size tire and my 3 ton jack, I was able to get to work the next day. When fixing the flat, I asked them to check my battery because when it was 120 degrees, the crank was not as strong and sure enough the battery was very weak, It was a costco battery and just at 35 months, so went there, got a full refund and got a new one (for $7 more!).

Now the car would not idle (I had taken the battery off, so the memory was gone). I fixed that by driving around for a while. Then cleaned my Throttle body the next day and then got a CEL. Took the battery off and the CEL is gone.

All started with a nail in the fwy. Moral of story, I should had paid more attention to the weak crank and not brushed it off. The new battery has a 4 yr warranty, so might as well change it before it is out of warranty.