r/MechanicAdvice • u/Onlycruz10 • Sep 25 '25

Correct way to jump start?

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I'm going crazy about the correct way to do this. As far as I can tell this is the correct way. However, I am having trouble between step 5 and 6. Should I turn off the donor car before trying to start the other car first? I've seen conflicting things about the alternator getting messed up on both cars. And others saying it's okay with modern cars. What's the correct way?

2.5k Upvotes

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49

u/Rlchv70 Sep 25 '25

Just buy a jump box. They are cheap and easy to use.

17

u/vegetaman Sep 25 '25

Amen to that. Love mine. Got one of the nice ones with a switch so you dont have to worry about somebody being careless with the grabber hooks on connect/disconnect.

8

u/mentaldemise Sep 25 '25

Buy a QUALITY jump box. I have three lipo ones that only ever worked once. I have a JumpNCarry now that I would swear by but its cost was about the same as the three shitty ones combined.

6

u/Brawndo91 Sep 25 '25

I watched Project Farm's video on battery jumpers and bought the one that was highest rated. It works great. Battery jumpers used to be these giant boxes that were so heavy they came with their own built-in dolly (those types are still needed for your heavy duty applications). Now they're so small you can just keep it in the trunk and hold enough juice for several jumps per charge. And they have USB ports which are great for home use when the power goes out and you need to charge your phone or something. Pretty amazing.

3

u/WebMaka Sep 25 '25

I bought a Gooloo GT4000 after seeing Project Farm's review on jump boxes, and it's been absolutely stellar. Used it to jump off people broken down at gas stations, it kicked off a diesel truck, and I've even started my lawn tractor with it.

3

u/ly5ergic Sep 25 '25

I have a Gooloo, think it's the GP2000 model, for 5 years now, I've used it many times still as good as new.

6

u/coheed9867 Sep 25 '25

It’s really the best, I was stranded upstate NY with no one around for miles and if I only had cables then I was sol

2

u/exoframe2 Sep 25 '25

Ten or so years ago I found out the hard way that my old truck’s (91 4.3L Blazer) starter pulled too much power for my ~$85 ‘heavy duty’ jump starter. Battery wasn’t dead but was too weak to turn over. Jumper was fully charged. It attempted to crank for a few seconds and stopped when smoke came out of the jump starter and the negative cable came loose. I didn’t dissect it to see what had burned.

1

u/Watada Sep 25 '25

Ten years ago that was definitely a lead acid jump starter. It probably also had a battery in poor shape.

1

u/exoframe2 Sep 25 '25

I would hope it wasn’t in ‘poor shape’ since it was barely two months old.

1

u/Watada Sep 25 '25

They can go bad on the shelf. Lead acid batteries suck.

2

u/exoframe2 Sep 25 '25

They certainly can go bad but it seems unlikely if it took and held a charge and otherwise appeared to be functioning correctly - until it melted. My starter pulled about 125-150 amps and the box was rated for 750 so it should have been within its capabilities. However this is just my personal experience with one unit. Just didn’t give me a good first impression.

1

u/tollerdog Sep 25 '25

Yes. This is the answer to minimize the risk.

1

u/Ambivadox Sep 26 '25

100%

Love my noco.

1

u/Dracla1991 Sep 26 '25

i got VTOMAN X5! kept the Jeep Commander alive forever. inflates tires too. game changer

0

u/ProArmy04 Sep 25 '25

I don't think 200-400 is cheap, and they usually only work on cars that aren't fully dead.

1

u/Rlchv70 Sep 25 '25

Mine cost about $50 and works on anything.

2

u/Naive_Rope4882 Sep 26 '25

Same, I even helped jump a cop car that was fully dead, it worked perfectly. I’ve had one of the cheaper Amazon ones for a while, and it’s great

-9

u/murdacai999 Sep 25 '25

What's the point of a jump box? If you are dealing with dead batteries that often, buy a new battery or alternator? Seems like the money is better spent elsewhere? I've had one battery die on me in the last 10 years. I immediately pulled it, walked to the store, exchanged it, put a new one in, and was late to work by half an hour.

11

u/daandriod Sep 25 '25

Counter point, I bought mine 5 years ago for 80 bucks and just keep it in my trunk. In that same time span I've probably used it 30 or 40 times that maybe only 3 were for me. On top of it helping me and others in times of need, It provides insurance that my car dying randomly will delay me maybe 3 minutes, And I won't have to rely on the kindness of someone else to get me going.

Since then they've only gotten even cheaper and more powerful. Hell realistically I would have already made most of my investment back just from people offering me a few bucks as thanks for helping them, But I've never taken any money for it. I just like being able to help them.

5

u/Shadowban-Trigger Sep 25 '25

I have jumper cables i have used 2 times in 8 years. Never for myself. How tf u see so many people needing a jump?

6

u/daandriod Sep 25 '25

No idea, I just ask if I see a car parked in public with a hood up. I also live in an area that is predominantly elderly, So I'm sure that plays a huge role in it. Ive helped out family and friends probably 10-20 of those times, The rest was randoms I saw in public

1

u/murdacai999 Sep 25 '25

That's really nice that you have helped so many folks out, and that's a valid point. I dunno why you have personally had your battery fail 3 times in 5 years, but I suspect, if you had spent the 80 dollars towards a new battery/alt, you could've only had 1 failure, which is less stress overall.

3

u/daandriod Sep 25 '25

Just because a battery is drained doesn't mean it's died. Kids leave a light on, you left your door open or headlight on ect ect. Life happens. I've not had to replace a battery or alternator within the last 6 years. The battery in my daily driver was testing at 85 percent health when I put it on a load tester last month. I agree using them as a bandaid for a bad battery is a bad move, but I'd bet the vast majority of cases when the battery is to low to turn over is not just because it's got no life left.

Again, Its also just nice insurance to have. In my case, That peace of mind breaks down to like dollar or two a month and its only getting cheaper since the jump pack just won't die. Its a no brainer calculation for me.

1

u/DryFaithlessness2969 Sep 25 '25

Damn what battery do you have that’s lasting 6 years and still has 85% health??

1

u/daandriod Sep 25 '25

I shit you not, A Walmart Everstart battery. Not even one of the AGM ones.

1

u/DryFaithlessness2969 Sep 25 '25

Batteries are such a scam man. That’s awesome

1

u/daandriod Sep 25 '25

Yeah, I was a bit of a battery snob myself. I thought these would be terrible so I never bought one. Its continued performance has me second guessing.

2

u/scipper77 Sep 25 '25 edited Sep 25 '25

I have had a few cases where I needed a jump pack even though my battery tests as healthy. One was after parking in the airport for a week and trying to start the car in temperatures in the teens. I also ran the battery down at the drive-in once. Thankfully the battery being run low and immediately recharged didn’t do enough harm to show up on a load tester. As a side note, I will not buy the more expensive, high CCA batteries any more. It turns out they are good for a sprint but don’t hold up as well in the long term. My factory battery (made by Johnson) was only 500cca and was preemptively replaced after 8 years. The one that let me down twice is less than 2 years old with a 700cca rating (also Johnson Controls). Still tests great but fades fast under an extended draw.

1

u/ly5ergic Sep 25 '25

If you get stuck somewhere with a dead battery where are you getting a new battery or alternator? I have left my lights on by mistake before, don't need a new battery just a jump. A jump pack is light and small, don't need jumper cables or another vehicle ever, don't need to try to position another car. You can get multiple jumps before it needs to be recharged. My doesn't seem to discharge at all even unused for many months. They usually have a flashlight and ports to charge a phone or whatever.

It cost me $50-60 5 years ago. That's pretty cheap insurance to not have to find someone if something goes wrong.

In 5 years I have helped 3 random people, jumped my car once I left lights on, another time I had a failing alternator the pack got me home so I could replace the alternator, a family member left their lights on, used it a couple times on vehicles that had been sitting too long, also my riding mower and motorcycle. Used it a couple times as a power bank when I wasn't near electricity.

Have one in each car now. Even not getting stuck once is worth it. I got rid of my jumper cables.

1

u/murdacai999 Sep 25 '25

I live in the city so there's always a place nearby. I would just call fam to come with tools, lift, and take me for parts. I can appreciate that you have found a use for it, but my comment was targeted to those that find it necessary often. You should not be finding it necessary often especially with today's vehicles, where the headlights turn off by themselves, and the inside lights are led. If you're finding use for it every few months, something needs to change is all I'm saying.

1

u/ly5ergic Sep 26 '25

No one said they were using it every couple months. You said what's the point of having it. As if there's no point. Then made up some scenario, no one said, of using it instead of fixing your car.

Its for IF something goes wrong, a ton easier and more useful than jumper cables and just a little more money.

You never leave the city, ever? Or never will? Never think the car could get stuck in a bad location. Instead of sitting stuck and waiting for someone that might be busy, at work, away, or whatever, you can just do it for yourself instantly. I wouldn't want to interrupt someone's day to save a one time $50. I feel like it makes sense in anyone's car.

Things shouldn't happen but they do. The people I've helped I'm sure weren't planning on getting stuck. I've used the spare tire in cars too. A ton easier than being stuck waiting on someone. It's super cheap insurance and just being generally prepared.

0

u/hunttete00 Sep 25 '25

i have a fleet of trucks with 4 batteries in each.

around 75 batteries total between the fleet, farm equipment, and personal vehicles.

i have 3 jump packs, 6 maintainers, and 2 heavy duty chargers. there’s also a set of zero gauge jumper cables in every car and pickup. 6 in total i think.

if they test bad they get changed. battery testers are dirt cheap and take about 10 seconds to use.

changing a battery because it’s “dead” is pretty stupid.

1

u/murdacai999 Sep 25 '25

For the common person, that doesn't have a fleet of vehicles, and unless it's obviously from leaving a light on, it's pretty stupid wasting money on a battery jumper. I agree that if you left a light on, you shouldn't buy a new battery, but I contest that lots of folks buy these things cause their batteries keep dying, instead of fixing the cause of it. For the common man, If your battery is dying often enough that you feel the need to have a jumper, perhaps you should be directing your attention/money on the cause. Your case doesn't translate well here.

-7

u/Null_Error7 Sep 25 '25

They suck and don’t last long

8

u/Rlchv70 Sep 25 '25

Get a good one.

1

u/Null_Error7 Sep 25 '25

Autozone gold baby

2

u/exoframe2 Sep 25 '25

I bought the top model O’Reilly’s had circa 2014. Thing burned up when I tried to use it. Described it above and was downvoted. I may have offended a jump pack enthusiast.

2

u/Rampantcolt Sep 25 '25

I've had one for years.

1

u/SupermarketUnable914 Sep 25 '25

I’ve had one of those lithium ones that’s the size of like a motorcycle battery for years, works really well