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Battery jump starters are one of the most useful items any driver should carry. Flat batteries are one of the most common breakdowns in any car or truck.
But there’s a lot of mystery about portable jump starters… how do they work, what size do I need and so on.
Have a browse through these FAQs and find out a whole lot more about jump starter packs for your car or truck. And if you have any other questions, please ask in the Comments at the end of this post.
We’ve also done a comprehensive review on our NOCO Genius Boost GB70 Portable Jump Starter. Go here for more information.
☞ How do battery jump starters work?
Portable or battery jump starters come with their own internal battery. They’re designed to provide a high current for a short amount of time, just like your car’s starting battery.
You simply connect the two clamps to the battery terminals, red to positive and black to negative. Press the On button on the jump starter, then start your vehicle.
Once the car starts, switch the jump starter off, disconnect the (red) positive clamp then disconnect the (black) negative clamp.
Note, they won’t charge your battery. They are designed only to provide the high current a car needs for starting.
Related questions
– How do I use a portable jump starter?
– How do I jump start a car without cables?
Yes, it will… but only if it has a Force Start or Override function.
The Override function provides additional power to a dead flat battery. If your battery has collapsed and it’s completely dead, you can still use the jump starter to start the vehicle.
The trade-off? The unit’s safety features which protect it from damage are disabled in this mode. So use this feature carefully.
Look for the Override feature when choosing a portable jump starter. Most cheap units do not have this function. However, Override has saved our skin many times. It really is essential, rather than an option.
Here’s 3 portable jump starters with the Override function:
– NOCO GB40 Boost Plus
– Projecta IS2000, 12/24V
– Projecta IS1220, 12V
The jump starter’s internal battery needs to be kept charged, so it’s ready for use. They’re charged using a mains (240VAC) plug or a USB plug, depending on the model.
A high quality jump starter will maintain its charge indefinitely. As a guide, if you haven’t used it for 6 months then check the charge level.
To give you an idea, the NOCO range will only lose 1 – 2% of its battery power per month if it’s not used. Look for a similar specification when buying.
The best battery jump starter is one that’s large enough to start your car! ☺️ See below for more details on how to size a jump starter. Generally, the more you pay the higher the quality.
Features to look for:
✔︎ Spark-proof. This is important, as lead-acid batteries (used in most vehicles) can give off explosive gases.
✔︎ Reverse polarity protection. This means if you connect the clamps to the wrong terminals, the jump starter will show a fault light and will not operate.
✔︎ Rechargeable from USB and 12V ports. Being rechargeable from mains power is also useful, but not necessary if it’s rechargeable from USB ports.
✔︎ Has an LED flashlight. This is priceless when you’re caught with a flat battery at night. And being LED, it won’t use much power. A flashing strobe function is also useful in an emergency. For example, if you’re broken down in a dangerous position at night, you can use this to warn other traffic.
✔︎ Has the ability to charge devices like phones from a USB outlet.
✔︎ Has a manual override feature which allows you to start batteries below 2 volts.
✔︎ Is lightweight and portable.
The best way is to look at the top of your battery and find the Cold Cranking Amps rating, or CCA. It will have “CCA xxx” somewhere on the battery’s label (xxx will be a number).
The CCA rating of a car battery should be on the battery’s label.
If not, have a look in the Electrical Specifications section of the vehicle’s Owners Manual or call your vehicle dealer or a battery sales outlet.
The CCA increases as the engine size increases, and diesel engines need a larger CCA rating than a petrol engine for the same engine size.
Also consider whether you might want something bigger than you need, in case you buy a larger vehicle in the future.
Once you’ve decided what CCA rating you need, choose a battery jump starter with a higher rating. This way, you can be sure it will start your car. Confusingly, the jump starter will be rated in Amps.
Say your battery’s rated at CCA 540. In this case, a jump starter rated at higher than 540A will be okay.
A NOCO Genius GB40 will start most cars. Just double-check the battery’s CCA rating against the jump starter’s amperage rating first (1,000A for the GB40).
Related questions
– How do you determine which portable battery jump starter to get for your car for emergencies?
– Which Noco Genius do I need?
Yes, you should always keep jumper cables or a portable jump starter in your car. Batteries have a tendency to fail at the least convenient moment… on a cold, rainy night in a deserted carpark or when you’re running late for that important meeting.
Should you buy jumper cables (also known as jumper leads) or a battery jump starter? The downside of jumper leads is you need a second vehicle to act as the starting vehicle.
Another consideration… many people are loathe to connect jumper leads to their vehicle, because jump starting has been known to damage the electronics in modern cars.
However, if you have a portable jump starter, then you’ll be self-contained. You don’t need someone to help you.
Most definitely… if you buy a quality unit. We’ve used ours dozens of times now and it has worked faultlessly every time.
We did have a set of jumper leads, but wouldn’t even consider going back to them now. The portable jump starters are so quick and easy to use, plus they have a whole lot of safety features.
No more concerns about connecting them wrongly, accidentally causing dangerous sparks or damaging the vehicle’s delicate electronics. Plus, you get a whole lot of extra features… USB charging for your devices, a flashlight and emergency strobe, and no more messy tangles of jumper cables taking up storage space.
Go here for a wide selection of quality jump starters and accessories.
A car battery charger slowly restores charge to a flat battery. It uses low current to gradually charge the battery. This can take several hours.
Note: If you want to know more about portable battery chargers, go here.
Battery chargers runs through several charging stages, optimising the charge in the battery. When finished the battery will be fully charged (assuming the battery’s not faulty).
A portable car battery charger is simply a small charger you can easily pick up and carry with you.
A portable jump starter does not charge your flat battery. It simply provides the high level of current needed to start your car. The jump starter is designed to provide short bursts of very high current.
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I bought a 2000 amp jump starter for my Pajero 3.2L Diesel.
First time I needed to use it, even though it showed 100% charge, it wouldn’t turn the engine over. RAC said my battery needed replacing which I did. Enquired with manufacturer why jump starter didn’t work and to my surprise was advised that they didn’t work on failed batteries.
So apparently only useful if good battery goes flat by leaving lights on etc, but no use if battery dies. I haven’t seen this mentioned on any advertising or documentation supplied with the unit or for that matter on any other brands. In future I won’t be going bush without a new battery, so probably wasted money buying the jump starter.
Hi Bernard,
I’m not quite sure why the manufacturer would say this. That doesn’t sound right. What brand is it?
We have 2x12V (24V system) batteries in our Isuzu truck. One was 100% dead and the other was almost dead. I attached one NOCO Genius GB70 to each battery and started the truck several times without issue.
Does your jump starter have the function to override its safety features (reverse polarity protection, etc), so you can start a completely dead battery?
You definitely shouldn’t need to carry a spare battery. That’s what the jump starter is for… to get you out of trouble (just as you thought when you bought it).
Any half-decent jump starter will start your vehicle when the battery is dead.
Cheers, Andrew
This “So apparently only useful if good battery goes flat by leaving lights on etc, but no use if battery dies. ” is the information I was looking for.
Should have been in the body of the advice above -Thanks Bernard
Hi Bernard,
No that’s not correct. A quality battery jump starter will start a vehicle with a dead battery. See my comment above.
Cheers, Andrew
I’m using a 1500 amp 12v vehicle jump starter by Battery Tender (fit’s in the glove box). I’m driving a 2000 Ford Excursion V10 motor. Unfortunately I’m having to wait to afford a new battery ave $390-$410, and my battery is so dead I can’t even get a charge on my phone if trucks not running. So every time I have to start the truck I have to use the jump box. And once it’s started I plug it up to recharge and I’ve been having to do this for almost 3 weeks now. So if your jump box is charged up, there’s no reason for it Not to start a dead flat line battery. And I don’t have any extra booster on this jump box for a flat line battery either. Maybe y’all should check out Adams Battery Tender jump box.
I bought a Nexpow 2000 battery jump starter. When I connected to a dead car battery, it beeps and shows r sc. I tried to figure out what that means but no luck. Do you know? Does it mean that the starter won’t be able to start a totally dead battery? I couldn’t find a website or contact info for the battery pack.
Hi,
You need a manual override button for when you need to jump start a completely dead battery. The Nexpow 2000 does not have this (very useful) feature.
Cheers, Andrew
Andrew, I’m thinking of using one of these jump starters as a high current source of 12v for my boat anchor winch (950w motor). It requires up to max of 80amps (varies from 10-80 with load) for about 2mins for a typical anchor raising. I have solar charging onboard with 12v outlets so I could easily charge from that I guess. Plus I’d have the flexibility to bring home for charging at the end of the day or weekend.
If this will work, it will save me a ton of weight (and a little money) and eliminating a need to find another charging source for a 2nd battery. My boat is only small and light and the engine is a little outboard.
What do you think?
Hi Neil,
Portable jump starters are designed to output maximum current for a very short time… just long enough to start a vehicle. The current drops off very quickly after the initial burst of power. If you’re trying to start a car, the jump starter internal battery needs time between starts to recover.
I love your idea, but you would only get power for a short time (10 or 20 seconds at most) before the jump starter shut down to protect its internal battery.
The other option could be to get one of those huge jump starter packs designed to start large truck diesel engines. But that would be way more expensive than a dedicated battery and possibly heavier. I’m guessing weight’s an issue on your boat, so it’s probably not an option.
Here’s a thought…
Depending on your budget, I’d probably choose a Lithium battery like this one instead. It’s only 8kg and has a maximum continuous discharge of 85A for 40 minutes. You could take it home and charge it afterwards.
Hope this helps.
Cheers, Andrew
That helps heaps Andrew. I’ll reconsider my plans.
Thank you!
Glad I could help! Cheers, Andrew
Hi Andrew. I’ve been looking for info on the different amp ratings they give, along with the displacement numbers. I’ve had no luck. Can you tell us about this please. For example, Tacklife has a line out, and they advertise numbers like 600A or 800A, and say it will start 7.0L vehicle. Then others say 1500A and 6.0L vehicle. – As well, most have a ‘peak’ amp rating, and a regular amp rating which is significantly lower. What to make of this, Idk?? Is ‘peak’ the boost that is possible if needed, the override feature you discussed? Meaning, I’m only getting the lower number ‘with’ safety features??? … Because what complicates is, I have a 5.7L Hemi, RAM Laramie, my battery is only 665 CCA. This implies that even the smallest units should start me no problem, but that is not the case. Going by what’s advertised in listings, I need at least a 1K-1200K amp starter …
So, basic question is what do I really need to look at, while searching for best value? How to calculate their amps in reality, and what I’ll get from it?? ….. I’ve watched many videos, searched for more, no one discusses this, so I feel like I’m missing the obvious, or the sector needs some attention, lol, Idk… ty, though
Peace
Hi,
I understand your frustration, it’s very confusing! Let me get back to you on this, as I want to answer your question properly.
Just one point. When I look up the battery size required for a 5.7L Hemi Laramie, I’m seeing it needs between a 750 and 850CCA battery. Is your existing battery undersized? Or am I missing something here?
The reason I ask is, I’d expect a 5.7L petrol motor to typically need around a 1,000A jump starter.
Cheers, Andrew
Hi. Well, I’m still working on it, and I think I understand a little better now. *I also found a dirty little secret about the EV industry … I couldn’t find the required starting amps for my truck, it’s not in the manual. I read a couple sites that talked about engines in general and both stated V8s need about 250-400 amps. So that’s the part I really need to answer first.
What I understand better now is what they mean with the numbers they put on the battery. And a lot of this is to do with where you live, and the cold weather. …. So, my battery, as you know, as in all cars, has a group number for size and orientation. Well, my group number, the lowest amps I can find is around 630cca. But that is actually only half of what the battery can put out, because cca is what the battery produces at -18 degrees C, which is half of it’s capacity. And the ca is what it produces at another temperature, 0 degrees Celsius. ….So the battery I have, it has 790cca, 1025 ca and 1580 amps at room temp. But the truck only needs maybe 400 amps to start. But, that’s a new engine. Oil sludgery, and cam friction builds up, and it might take more, and if your oil is low, or you have thick weight in there, and it is really cold, it can double the amount required, all things being strained, so the mid 600s is just being safe for our climate here. BUT that is lead acid, lol. … From what I understand lithium does not drop as much as lead acid, but IDK how much it does drop. I think though, if they are calling it cca, then they should mean the jumppack itself, is acclimated at -18. They do not all say CCA though, now I have to note that when looking.
* That was the dirty secret though. While lithium does not drop as much, it does lose a lot of it’s performance at cold temps, and can even shut down. They also can take 8-10x as long to charge in sub-zero temps. Idk, to me that pretty much makes it a non-sequitur, EVs cannot service most developed nations.
peace
You’ve been busy!
I agree, sizing a battery jump starter correctly can be difficult. It’s a whole topic on its own and beyond the scope of these FAQs.
And you’re spot on – battery output depends on ambient temperature, age of the battery, state of charge, plus a whole lot of other factors (like how thick the oil is when cold for example). Using CCA is a good guide because it gives you a buffer… the battery’s not working at its limit all the time.
In summary, it’s best to stick with the known jump starter brands (NOCO, Projecta, and so on) rather than the cheaper brands. Reputable brands will state maximum recommended engine capacity (for diesel and petrol engines) for each model of jump starter. These are a good guide. If in doubt, spend a bit more and get the next size up.
As a general comment… cheaper brands are cheap for a reason. They might have a smaller internal battery, smaller cables, cheap components, and so on. And often their claimed capacities are exaggerated. In this case, choosing a much bigger model than you think you’ll need is probably the best option.
Far better to spend a little more up front than be stuck in the middle of nowhere.
Cheers, Andrew
I purchased a Thunder brand jump starter. Went to use it today and found the cover on the product is being forced off the appliance by what appears to be the battery expanding inside the casing. Is this dangerous?
Hi Ray,
That’s usually caused by gases building up inside the battery. It’s potentially dangerous, as the battery could catch fire depending on the battery type. Lithium-ion (not LiFePo4) batteries are the main culprits. Don’t try to remove the battery.
Take the whole jump starter to an e-waste collection site or a car battery supplier if there’s one in your area. Don’t throw it in the general waste bin.
Hope this helps. Cheers, Andrew
Hi Andrew
Always informative, the info you provide, thanks.
My question is like you, I have 2x12volt batteries for my isuzu 75/155, do I need two jump starters? I am technically challanged on electrics, my apoligies.
Is it possible send an email with your response, thanks.
Hi Neil,
I’m glad it was helpful. Yes, you need 2 two jump starters because you need to attach one to each battery. There are a couple of monster 24V jump starters available, but they’re too big (and expensive) to carry around.
Cheers, Andrew
Can I use a lithium ion jump starter to jump an amg battery?
Yes you can. Cheers, Andrew
Hi Andrew, I stumbled onto this forum after a very frustrating search for answers to the question of whether the “smart” portable jump units with reverse polarity protection can somehow still provide a power surge sufficient to blow the main “max” fuse on a 2010 Honda Fit.
I parked this perfectly-running car in an airport long-term lot and returned a week later to find the battery dead, so I contacted roadside assistance. The technician first attempted to use a “smart” portable jump unit with reverse polarity protection.
On the first attempt to start the car, the running lights came on very briefly, but the car didn’t turn over at all. Every subsequent attempt to start the vehicle failed (including using a more powerful jump unit, and finally attempting to swap out the battery). There were never any other signs of life after the running lights flash on the first attempt.
I had to have it towed to my mechanic who found the Max Fuse Assembly had been blown, and the repair was not cheap. I should mention that the kid that tried to jump my car seemed quite unsure of himself and kind of fumbled around, and also admitted that he attached the jump unit to the wrong terminals at first.
The tow company claims it would be impossible for their charge unit to cause damage because of the reverse polarity protection on all their portable jump units. Is that really true? Any feedback on this would be greatly appreciated. Thanks much and cheers to you! 🙂 Sue
Hi Sue,
Any reasonable quality battery jump starter should have reverse polarity protection. It should have a light – green to indicate correct connection and red to indicate reverse polarity.
When the battery jump starter detects reverse polarity, it should instantly isolate the power from the cables and illuminate the red light. So effectively the battery jump starter isn’t connected to the battery, as it’s isolated internally in the jump starter pack.
But from what you describe, it sounds very much like the jump starter did indeed blow the max fuse. Maybe their battery jump starter was faulty, or doesn’t have reverse polarity protection.
The problem is, there’s no way for you to prove this.
Believe me, I know how incredibly frustrating it is when something like this happens. It’s your word against theirs and there’s really not much more you can do about it. The only thing I’d suggest is talking to your mechanic. What do they think?
Hope this helps.
Cheers, Andrew